Computer math -- update

tcmedara said:

Forgot I'd sent a post off to Cateye regarding the time, distance, and ave
speed mismatches on my Enduro 2 cyclocomputer (or "bull skirt" as S o r n i
calls it).

Got the response today. For those who care:

Quoted message said:

Hi Tom

It has to do with how frequently the unit updates the information it is

receiving. For instance, current speed may be updated every x seconds, where
as the >calculation for average speed may be performed every y seconds. I
believe the calculation for current is performed much more frequently than
that for average, >hence this discrepancy. This, in effect, would make the
current speed data marginally more accurate that the average speed data, but
they are both pretty reliable.

Quoted message said:

(snip ID info)

Quoted message said:

Thanks for supporting Cat Eye!!!"

Interesting. I would have thought it was a pretty continuous process.

Tom

Dear Tom,

I'm a little disappointed with vague X versus Y times from a
manufacturer. I'd expect an actual engineer to give specific
times.

I'm also still puzzled by the idea that the average speed
will somehow vary according to how often it's calculated
when the elapsed time is 60 minutes and the elapsed distance
is 5.00 miles--what's that got to do with current speed?
What calculation at sixty minutes and five miles can make it
anything but 5.00 mph average?

While I hesitate to say marketing blather, I'd have handed
an essay like that back and told the student to give an
example and some numbers to explain how the average speed
ended up something other than 5 mph after five miles in an
hour.

Try not to dispel my happy illusion that the students only
pulled such stuff on the English department and saved their
sensible efforts for the sciences.

Carl Fogel

Quoted message said:

On Mon, 27 Sep 2004 19:04:10 -0400, "tcmedara"
<[email hidden]> wrote:

Quoted message said:

Forgot I'd sent a post off to Cateye regarding the time, distance, and ave
speed mismatches on my Enduro 2 cyclocomputer (or "bull skirt" as S o r n

i

Quoted message said:

calls it).

Got the response today. For those who care:

Quoted message said:

Hi Tom

It has to do with how frequently the unit updates the information it is

receiving. For instance, current speed may be updated every x seconds,

where

Quoted message said:

as the >calculation for average speed may be performed every y seconds. I
believe the calculation for current is performed much more frequently than
that for average, >hence this discrepancy. This, in effect, would make the
current speed data marginally more accurate that the average speed data,

but

Quoted message said:

they are both pretty reliable.

Quoted message said:

(snip ID info)

Quoted message said:

Thanks for supporting Cat Eye!!!"

Interesting. I would have thought it was a pretty continuous process.

Tom

Dear Tom,

I'm a little disappointed with vague X versus Y times from a
manufacturer. I'd expect an actual engineer to give specific
times.

I doubt my question ever got to a real engineer. I'm sure this is the
response of the front line customer service gatekeeper who is given enough
knowledge of the product to discourage further inquiry. I was amused by the
"may be performed every y seconds" comment. I'm not sure if he's just
making it up or just couldn't express is point well.

Quoted message said:

I'm also still puzzled by the idea that the average speed
will somehow vary according to how often it's calculated
when the elapsed time is 60 minutes and the elapsed distance
is 5.00 miles--what's that got to do with current speed?
What calculation at sixty minutes and five miles can make it
anything but 5.00 mph average?

Hence my question! All I can think of is that the computer itself computes
average speed based on a sampling of current speed at set intervals rather
than a straight-up calculation of distance over time. If I thought it worth
the effort I'd re-engage with Cateye. As it stands, I was merely curious to
see if and how they would respond.

Quoted message said:

While I hesitate to say marketing blather, I'd have handed
an essay like that back and told the student to give an
example and some numbers to explain how the average speed
ended up something other than 5 mph after five miles in an
hour.

I don't hesitate to say it at all. As a matter of fact, I replied to the
man and told him I thought the term "pretty reliable" was a bit subjective
when talking about computer calculations.

Quoted message said:

Try not to dispel my happy illusion that the students only
pulled such stuff on the English department and saved their
sensible efforts for the sciences.

Please maintain your illusions Carl. As I said previously, I don't think
there was much engineering effort that went into the response. I think the
anonymous Cateye customer service rep viewed his response as one of creative
license rather than technical accuracy. This is obviously what happens to
all those Humanities majors that were having such a good time in college
while the engineering students slaved away in the lab.

Tom

Quoted message said:

tcmedara said:

Got the response today. For those who care:

It has to do with how frequently the unit updates the information it
is receiving. For instance, current speed may be updated every x
seconds, where as the >calculation for average speed may be
performed every y seconds. I believe the calculation for current is
performed much more frequently than that for average, >hence this
discrepancy. This, in effect, would make the current speed data
marginally more accurate that the average speed data, but they are
both pretty reliable.

I'm also still puzzled by the idea that the average speed will
somehow vary according to how often it's calculated when the elapsed
time is 60 minutes and the elapsed distance is 5.00 miles--what's
that got to do with current speed? What calculation at sixty
minutes and five miles can make it anything but 5.00 mph average?

This is really interesting. I had always wondered if cycle computers
calculated average speed the way I do (distance/time) or if a
statistical sampling method was used to calculate average speed. The
reason I've wondered this is that average speed calculations using the
normal distance/time formula has frequently resulted in a different
answer than the cycle computer calculates.

The reply from Cateye seems to indicate that in fact they use the
periodic sampling method. This is probably done so that the computer
isn't running that calculation constantly to keep the display updated.
After all, this is a pretty low-power computer and running calculation
periodically rather than constantly reduces both demands on the CPU
and battery drain. Of course, "X seconds" for calculating current
speed might be .10 seconds and "Y seconds" for average speed might be
5 seconds. Who knows?

Tim McNamara said:

Quoted message said:

tcmedara said:

Got the response today. For those who care:

It has to do with how frequently the unit updates the information it
is receiving. For instance, current speed may be updated every x
seconds, where as the >calculation for average speed may be
performed every y seconds. I believe the calculation for current is
performed much more frequently than that for average, >hence this
discrepancy. This, in effect, would make the current speed data
marginally more accurate that the average speed data, but they are
both pretty reliable.

I'm also still puzzled by the idea that the average speed will
somehow vary according to how often it's calculated when the elapsed
time is 60 minutes and the elapsed distance is 5.00 miles--what's
that got to do with current speed? What calculation at sixty
minutes and five miles can make it anything but 5.00 mph average?

This is really interesting. I had always wondered if cycle computers
calculated average speed the way I do (distance/time) or if a
statistical sampling method was used to calculate average speed. The
reason I've wondered this is that average speed calculations using the
normal distance/time formula has frequently resulted in a different
answer than the cycle computer calculates.

The reply from Cateye seems to indicate that in fact they use the
periodic sampling method. This is probably done so that the computer
isn't running that calculation constantly to keep the display updated.
After all, this is a pretty low-power computer and running calculation
periodically rather than constantly reduces both demands on the CPU
and battery drain. Of course, "X seconds" for calculating current
speed might be .10 seconds and "Y seconds" for average speed might be
5 seconds. Who knows?

CatEye computers also calculate speed as an average over a period of a
few seconds. This can be seen when accelerating down a steep grade from
an initially low speed, as the MPH does not changed for several seconds
at a time.

--
Tom Sherman

[email hidden said:

"]

I'm also still puzzled by the idea that the average speed
will somehow vary according to how often it's calculated
when the elapsed time is 60 minutes and the elapsed distance
is 5.00 miles--what's that got to do with current speed?
What calculation at sixty minutes and five miles can make it
anything but 5.00 mph average?

Carl Fogel

Dear Carl:

Cateye's response isn't necessarily hokum. Whether or not it's true is still questionable but it is not logically inconsistant with any of the known facts in this case.

It could be that the average speed function hadn't yet been updated to reflect the most current time and distance readings. Imagine riding at 15.1 miles per hour for 59 minutes and 30 seconds - you would have travelled 14.97 miles. Then in the next 30 seconds you travel at 3.6 mph and go 0.03 miles. Your distance would read 15.00 miles and your time would read 60 minutes and 00 seconds. But if your average speed were calculated once every 30 seconds, and it hadn't been updated since the 59m30s calc - the average speed would still read 15.1 mph.

I'm sure the statistical sampling method isn't used - that would require storage of large amounts of data, where recalculation every few seconds does not - and is more accurate by definition.

[email hidden] wrote in message news:<[email hidden]>...

Quoted message said:

tcmedara said:

Forgot I'd sent a post off to Cateye regarding the time, distance, and ave
speed mismatches on my Enduro 2 cyclocomputer (or "bull skirt" as S o r n i
calls it).

Got the response today. For those who care:

Quoted message said:

Hi Tom

It has to do with how frequently the unit updates the information it is

receiving. For instance, current speed may be updated every x seconds, where
as the >calculation for average speed may be performed every y seconds. I
believe the calculation for current is performed much more frequently than
that for average, >hence this discrepancy. This, in effect, would make the
current speed data marginally more accurate that the average speed data, but
they are both pretty reliable.

Quoted message said:

(snip ID info)

Quoted message said:

Quoted message said:

Thanks for supporting Cat Eye!!!"

Interesting. I would have thought it was a pretty continuous process.

Tom

Dear Tom,

I'm a little disappointed with vague X versus Y times from a
manufacturer. I'd expect an actual engineer to give specific
times.

I'm also still puzzled by the idea that the average speed
will somehow vary according to how often it's calculated
when the elapsed time is 60 minutes and the elapsed distance
is 5.00 miles--what's that got to do with current speed?
What calculation at sixty minutes and five miles can make it
anything but 5.00 mph average?

While I hesitate to say marketing blather, I'd have handed
an essay like that back and told the student to give an
example and some numbers to explain how the average speed
ended up something other than 5 mph after five miles in an
hour.

Try not to dispel my happy illusion that the students only
pulled such stuff on the English department and saved their
sensible efforts for the sciences.

Carl Fogel

Dear Carl,

Not marketing blather - has to do with sampling rates and a construct
known as a moving average. The average on a bike computer is averaged
over a set of samples of the current speed (which is actually an
average given that it really isn't instantaneous but rather a
calculation based on the circumference of the wheel and the time it
takes for the wheel to go around once). So the average is an average
of N instances of the average speed for a wheel to revolve once
completely. Instantaneous, continuous measures are strictly the realm
of analog devices.

Variations from the "expected" result of continuous measures are,
well, to be expected.

Your suggestion that this method for producing digital measures of
speed is somehow wrong or suitable only for the English department
suggests a personal failing on your part. Perhaps a short course in
DAC/ADC devices would be appropriate?

Pedantically yours,

App, who suggests similar deficits may exist elsewhere in your
education as evidenced by your political leanings.

[email hidden] wrote in message news:<[email hidden]>...

Quoted message said:

tcmedara said:

Forgot I'd sent a post off to Cateye regarding the time, distance, and ave
speed mismatches on my Enduro 2 cyclocomputer (or "bull skirt" as S o r n i
calls it).

Got the response today. For those who care:

Quoted message said:

Hi Tom

It has to do with how frequently the unit updates the information it is

receiving. For instance, current speed may be updated every x seconds, where
as the >calculation for average speed may be performed every y seconds. I
believe the calculation for current is performed much more frequently than
that for average, >hence this discrepancy. This, in effect, would make the
current speed data marginally more accurate that the average speed data, but
they are both pretty reliable.

Quoted message said:

(snip ID info)

Quoted message said:

Quoted message said:

Thanks for supporting Cat Eye!!!"

Interesting. I would have thought it was a pretty continuous process.

Tom

Dear Tom,

I'm a little disappointed with vague X versus Y times from a
manufacturer. I'd expect an actual engineer to give specific
times.

I'm also still puzzled by the idea that the average speed
will somehow vary according to how often it's calculated
when the elapsed time is 60 minutes and the elapsed distance
is 5.00 miles--what's that got to do with current speed?
What calculation at sixty minutes and five miles can make it
anything but 5.00 mph average?

While I hesitate to say marketing blather, I'd have handed
an essay like that back and told the student to give an
example and some numbers to explain how the average speed
ended up something other than 5 mph after five miles in an
hour.

Try not to dispel my happy illusion that the students only
pulled such stuff on the English department and saved their
sensible efforts for the sciences.

Carl Fogel

Dear Carl,

Not marketing blather - has to do with sampling rates and a construct
known as a moving average. The average on a bike computer is averaged
over a set of samples of the current speed (which is actually an
average given that it really isn't instantaneous but rather a
calculation based on the circumference of the wheel and the time it
takes for the wheel to go around once). So the average is an average
of N instances of the average speed for a wheel to revolve once
completely. Instantaneous, continuous measures are strictly the realm
of analog devices.

Variations from the "expected" result of continuous measures are,
well, to be expected.

Your suggestion that this method for producing digital measures of
speed is somehow wrong or suitable only for the English department
suggests a personal failing on your part. Perhaps a short course in
DAC/ADC devices would be appropriate?

Pedantically yours,

App, who suggests similar deficits may exist elsewhere in your
education as evidenced by your political leanings.

DiabloScott said:

Quoted message said:

I'm also still puzzled by the idea that the average speed
will somehow vary according to how often it's calculated
when the elapsed time is 60 minutes and the elapsed distance
is 5.00 miles--what's that got to do with current speed?
What calculation at sixty minutes and five miles can make it
anything but 5.00 mph average?

Carl Fogel

Dear Carl:

Cateye's response isn't necessarily hokum. Whether or not it's true is
still questionable but it is not logically inconsistant with any of the
known facts in this case.

It could be that the average speed function hadn't yet been updated to
reflect the most current time and distance readings. Imagine riding at
15.1 miles per hour for 59 minutes and 30 seconds - you would have
travelled 14.97 miles. Then in the next 30 seconds you travel at 3.6
mph and go 0.03 miles. Your distance would read 15.00 miles and your
time would read 60 minutes and 00 seconds. But if your average speed
were calculated once every 30 seconds, and it hadn't been updated since
the 59m30s calc - the average speed would still read 15.1 mph.

I'm sure the statistical sampling method isn't used - that would
require storage of large amounts of data, where recalculation every few
seconds does not - and is more accurate by definition.

Dear Diablo,

I suspect that your idea, though ingenious, doesn't explain
the actual situation.

Yes, a rider could travel at a higher average speed for most
of the trip and then slow down during the last 29 seconds,
just before the next half-minute re-calculation of the
average speed.

Yes, this would preserve a higher-than-actual average speed.

And yes, It works for your example of displaying a 15.1 mph
average when the true average is 15.0 mph.

But it works only if you slow to a crawl in the last 30
seconds and sample only every 30 seconds.

And it won't work if we go 5.4 mph for 59:30 and want to
cover 5.00 miles in an hour, unless we do some time travel
or ride backwards..

At 5.4 mph, we cover 5.00 miles in about 55:30.

So we'd have spend the last four-and-a-half minutes stopped
dead an inch from the finish line to preserve a 5.4 mph
average.

A 4.5 minute sampling time is unlikely to explain things.

Frankly, I'm doubtful of claims that the average is updated
only every 30 seconds to save batteries. The calculation is
trivial (current distance divided by current elapsed time)
and the speedometer is constantly updating all the other
functions.

I also doubt that tiny computations every three seconds or
so (roughly the sampling rate for the speed function) is
what drains the battery. The display's turn-off function
suggests that running the LCD is what really drains the
battery, not twenty calculations per minute. But maybe
someone who knows more about circuits will surprise me by
revealing that the calculations are trickier than I think.

Carl Fogel

On 28 Sep 2004 10:22:13 -0700, [email hidden]

(Appkiller) said:

[email hidden] wrote in message news:<[email hidden]>...

Quoted message said:

tcmedara said:

Forgot I'd sent a post off to Cateye regarding the time, distance, and ave
speed mismatches on my Enduro 2 cyclocomputer (or "bull skirt" as S o r n i
calls it).

Got the response today. For those who care:

>Hi Tom
>
>It has to do with how frequently the unit updates the information it is
receiving. For instance, current speed may be updated every x seconds, where
as the >calculation for average speed may be performed every y seconds. I
believe the calculation for current is performed much more frequently than
that for average, >hence this discrepancy. This, in effect, would make the
current speed data marginally more accurate that the average speed data, but
they are both pretty reliable.

>(snip ID info)

Quoted message said:

>Thanks for supporting Cat Eye!!!"

Interesting. I would have thought it was a pretty continuous process.

Tom

Dear Tom,

I'm a little disappointed with vague X versus Y times from a
manufacturer. I'd expect an actual engineer to give specific
times.

I'm also still puzzled by the idea that the average speed
will somehow vary according to how often it's calculated
when the elapsed time is 60 minutes and the elapsed distance
is 5.00 miles--what's that got to do with current speed?
What calculation at sixty minutes and five miles can make it
anything but 5.00 mph average?

While I hesitate to say marketing blather, I'd have handed
an essay like that back and told the student to give an
example and some numbers to explain how the average speed
ended up something other than 5 mph after five miles in an
hour.

Try not to dispel my happy illusion that the students only
pulled such stuff on the English department and saved their
sensible efforts for the sciences.

Carl Fogel

Dear Carl,

Not marketing blather - has to do with sampling rates and a construct
known as a moving average. The average on a bike computer is averaged
over a set of samples of the current speed (which is actually an
average given that it really isn't instantaneous but rather a
calculation based on the circumference of the wheel and the time it
takes for the wheel to go around once). So the average is an average
of N instances of the average speed for a wheel to revolve once
completely. Instantaneous, continuous measures are strictly the realm
of analog devices.

Variations from the "expected" result of continuous measures are,
well, to be expected.

Your suggestion that this method for producing digital measures of
speed is somehow wrong or suitable only for the English department
suggests a personal failing on your part. Perhaps a short course in
DAC/ADC devices would be appropriate?

Pedantically yours,

App, who suggests similar deficits may exist elsewhere in your
education as evidenced by your political leanings.

Dear App,

Are you saying that the speedometer is secretly storing N
instances of average speeds and then averaging them to
produce an apparent average speed?

If so, can you give N plausible figures that will produce an
apparent average speed of 5.4 mph when the rider covers 5.00
miles in 60:00 minutes?

And why would this strange method involving storing N sets
of data be used instead of simply recalculating the true
average every three to six seconds by dividing the current
distance by the elapsed time? Both figures are constantly
available, need no extra storage or calculations, and will
provide an accurate average speed for the trip.

Carl Fogel (who wonders if your theory is not only fake, but
inaccurate)

Appkiller said:

[email hidden] wrote in message

news:<[email hidden]>...

Quoted message said:

Quoted message said:

tcmedara said:

Forgot I'd sent a post off to Cateye regarding the time, distance,

and ave

Quoted message said:

Quoted message said:

Quoted message said:

speed mismatches on my Enduro 2 cyclocomputer (or "bull skirt" as

S o r n i

Quoted message said:

Quoted message said:

Quoted message said:

calls it).

Got the response today. For those who care:

>Hi Tom
>
>It has to do with how frequently the unit updates the information

it is

Quoted message said:

Quoted message said:

Quoted message said:

receiving. For instance, current speed may be updated every x

seconds, where

Quoted message said:

Quoted message said:

Quoted message said:

as the >calculation for average speed may be performed every y

seconds. I

Quoted message said:

Quoted message said:

Quoted message said:

believe the calculation for current is performed much more

frequently than

Quoted message said:

Quoted message said:

Quoted message said:

that for average, >hence this discrepancy. This, in effect, would

make the

Quoted message said:

Quoted message said:

Quoted message said:

current speed data marginally more accurate that the average speed

data, but

Quoted message said:

Quoted message said:

Quoted message said:

they are both pretty reliable.

>(snip ID info)

Quoted message said:

>Thanks for supporting Cat Eye!!!"

Interesting. I would have thought it was a pretty continuous

process.

Quoted message said:

Quoted message said:

Quoted message said:

Tom

Dear Tom,

I'm a little disappointed with vague X versus Y times from a
manufacturer. I'd expect an actual engineer to give specific
times.

I'm also still puzzled by the idea that the average speed
will somehow vary according to how often it's calculated
when the elapsed time is 60 minutes and the elapsed distance
is 5.00 miles--what's that got to do with current speed?
What calculation at sixty minutes and five miles can make it
anything but 5.00 mph average?

While I hesitate to say marketing blather, I'd have handed
an essay like that back and told the student to give an
example and some numbers to explain how the average speed
ended up something other than 5 mph after five miles in an
hour.

Try not to dispel my happy illusion that the students only
pulled such stuff on the English department and saved their
sensible efforts for the sciences.

Carl Fogel

Dear Carl,

Not marketing blather - has to do with sampling rates and a construct
known as a moving average. The average on a bike computer is

averaged

Quoted message said:

over a set of samples of the current speed (which is actually an
average given that it really isn't instantaneous but rather a
calculation based on the circumference of the wheel and the time it
takes for the wheel to go around once). So the average is an average
of N instances of the average speed for a wheel to revolve once
completely. Instantaneous, continuous measures are strictly the

realm

Quoted message said:

of analog devices.

As everyone knows, the moving average is a lowpass filter with
frequency response given by:
H(omega)=(1/L)(1-e^(-j*omega*L))/(1-e^(-j*omega))
and has nothing to do with "average" speed. What makes you think a
cyclocomputer calculates a moving average?

Quoted message said:

Variations from the "expected" result of continuous measures are,
well, to be expected.

Your suggestion that this method for producing digital measures of
speed is somehow wrong or suitable only for the English department
suggests a personal failing on your part. Perhaps a short course in
DAC/ADC devices would be appropriate?

What in the world do DACs and ADCs have to do with a cyclocomputer?
I will tell you: not a damn thing. What in the world are you talking
about?

A cyclocomputer is a frequency counter/interval timer/totalizer.

Quoted message said:

Pedantically yours,

App, who suggests similar deficits may exist elsewhere in your
education as evidenced by your political leanings.

Better study harder App!
--
Jim "wouldn't know a contour integral from a convolution sum" S.

On 28 Sep 2004 13:21:29 -0700, [email hidden]

Quoted message said:

Appkiller said:

[email hidden] wrote in message

news:<[email hidden]>...

Quoted message said:

Quoted message said:

On Mon, 27 Sep 2004 19:04:10 -0400, "tcmedara"
<[email hidden]> wrote:

>Forgot I'd sent a post off to Cateye regarding the time, distance,

and ave

Quoted message said:

Quoted message said:

>speed mismatches on my Enduro 2 cyclocomputer (or "bull skirt" as

S o r n i

Quoted message said:

Quoted message said:

>calls it).
>
>Got the response today. For those who care:
>
>>Hi Tom
>>
>>It has to do with how frequently the unit updates the information

it is

Quoted message said:

Quoted message said:

>receiving. For instance, current speed may be updated every x

seconds, where

Quoted message said:

Quoted message said:

>as the >calculation for average speed may be performed every y

seconds. I

Quoted message said:

Quoted message said:

>believe the calculation for current is performed much more

frequently than

Quoted message said:

Quoted message said:

>that for average, >hence this discrepancy. This, in effect, would

make the

Quoted message said:

Quoted message said:

>current speed data marginally more accurate that the average speed

data, but

Quoted message said:

Quoted message said:

>they are both pretty reliable.
>
>>(snip ID info)

>>Thanks for supporting Cat Eye!!!"
>
>Interesting. I would have thought it was a pretty continuous

process.

Quoted message said:

Quoted message said:

>
>Tom
>

Dear Tom,

I'm a little disappointed with vague X versus Y times from a
manufacturer. I'd expect an actual engineer to give specific
times.

I'm also still puzzled by the idea that the average speed
will somehow vary according to how often it's calculated
when the elapsed time is 60 minutes and the elapsed distance
is 5.00 miles--what's that got to do with current speed?
What calculation at sixty minutes and five miles can make it
anything but 5.00 mph average?

While I hesitate to say marketing blather, I'd have handed
an essay like that back and told the student to give an
example and some numbers to explain how the average speed
ended up something other than 5 mph after five miles in an
hour.

Try not to dispel my happy illusion that the students only
pulled such stuff on the English department and saved their
sensible efforts for the sciences.

Carl Fogel

Dear Carl,

Not marketing blather - has to do with sampling rates and a construct
known as a moving average. The average on a bike computer is

averaged

Quoted message said:

over a set of samples of the current speed (which is actually an
average given that it really isn't instantaneous but rather a
calculation based on the circumference of the wheel and the time it
takes for the wheel to go around once). So the average is an average
of N instances of the average speed for a wheel to revolve once
completely. Instantaneous, continuous measures are strictly the

realm

Quoted message said:

of analog devices.

As everyone knows, the moving average is a lowpass filter with
frequency response given by:
H(omega)=(1/L)(1-e^(-j*omega*L))/(1-e^(-j*omega))
and has nothing to do with "average" speed. What makes you think a
cyclocomputer calculates a moving average?

Quoted message said:

Variations from the "expected" result of continuous measures are,
well, to be expected.

Your suggestion that this method for producing digital measures of
speed is somehow wrong or suitable only for the English department
suggests a personal failing on your part. Perhaps a short course in
DAC/ADC devices would be appropriate?

What in the world do DACs and ADCs have to do with a cyclocomputer?
I will tell you: not a damn thing. What in the world are you talking
about?

A cyclocomputer is a frequency counter/interval timer/totalizer.

Quoted message said:

Pedantically yours,

App, who suggests similar deficits may exist elsewhere in your
education as evidenced by your political leanings.

Better study harder App!

Dear Jim,

In a daring move that I can't recommend to the folks at
home, I examined my $14.95 Nashbar cyclocomputer at the end
of today's ride.

As I suspected, it offers an average speed function.

It guessed that my average speed was 18.2 mph.

This is reasonably close to the result of 18.22 mph
suggested by its recording of 50:01 minutes (damned east
wind) and 15.19 miles.

My speed varied from a maximum of 34.8 (damned east wind) to
a minute stopped at the only traffic light.

If my no-name house-brand speedometer can do that well over
a far greater range of speeds in roughly the same time
period, I have to wonder if the Cateye whose average speed
started this thread is just plain buggy.

Later today, I plan to see how well the Fury RoadMaster's
new Schwinn speedometer does for roughly 4 miles and just
under 13 minutes.

Carl Fogel

Quoted message said:

Later today, I plan to see how well the Fury RoadMaster's
new Schwinn speedometer does for roughly 4 miles and just
under 13 minutes.

Carl Fogel

Maybe try to estimate the average speed recalc rate as well. I agree
it's probably every few seconds, rather than every thirty.

--
My bike blog:
http://diabloscott.blogspot.com/

Diablo Scott said:

Quoted message said:

Later today, I plan to see how well the Fury RoadMaster's
new Schwinn speedometer does for roughly 4 miles and just
under 13 minutes.

Carl Fogel

Maybe try to estimate the average speed recalc rate as well. I agree
it's probably every few seconds, rather than every thirty.

Dear Diablo,

I set the Schwinn speedometer to show average and set off.

Judging by my muttered count as the average changed, it's
updated roughly every 10 seconds--no reading at all for the
first ten seconds and then large jumps every ensuing ten
seconds to around 17 mph, at which point progress slowed
noticeably.

There were no interruptions, so once the Fury RoadMaster was
up to crusing speed, it was just a matter of cursing the
wind and the slight rise to the backstretch behind the zoo.

Eventually, the average reading exceeded 19 mph and the
little +/- indicating whether I was over or under began
chiding me now and then, as if I couldn't see the
speedometer dropping every so often.

At the end of the ride, the clock showed 12:16, the
astonishing trip meter showed 4.015 miles, and the
cyclocomputer offered to bet me that I had averaged 19.7
mph.

To my horror, this seems inaccurate, since (4.015 mph x 3600
seconds/hour ) divided by 736 seconds is only 19.638 mph,
not 19.7 mph. (Another ten seconds or quarter-turn of the
front tire might have led to a more honest and believable
estimate.)

I shall cast a jaundiced eye on the Schwinn's overblown
claims in the future, even though it's hardly inflating 5.0
mph to 5.4 mph like some instruments that I scorn to
mention.

Carl Fogel

Quoted message said:

Diablo Scott said:

Quoted message said:

Later today, I plan to see how well the Fury RoadMaster's
new Schwinn speedometer does for roughly 4 miles and just
under 13 minutes.

Carl Fogel

Maybe try to estimate the average speed recalc rate as well. I

agree

Quoted message said:

Quoted message said:

it's probably every few seconds, rather than every thirty.

Dear Diablo,

I set the Schwinn speedometer to show average and set off.

Judging by my muttered count as the average changed, it's
updated roughly every 10 seconds--no reading at all for the
first ten seconds and then large jumps every ensuing ten
seconds to around 17 mph, at which point progress slowed
noticeably.

There were no interruptions, so once the Fury RoadMaster was
up to crusing speed, it was just a matter of cursing the
wind and the slight rise to the backstretch behind the zoo.

Eventually, the average reading exceeded 19 mph and the
little +/- indicating whether I was over or under began
chiding me now and then, as if I couldn't see the
speedometer dropping every so often.

At the end of the ride, the clock showed 12:16, the
astonishing trip meter showed 4.015 miles, and the
cyclocomputer offered to bet me that I had averaged 19.7
mph.

To my horror, this seems inaccurate, since (4.015 mph x 3600
seconds/hour ) divided by 736 seconds is only 19.638 mph,
not 19.7 mph. (Another ten seconds or quarter-turn of the
front tire might have led to a more honest and believable
estimate.)

Well, first of all, 4.015 * 3600 / 736 is 19.64 NOT 19.638.
Second, assuming the Fury RoadMaster has normal sized wheels
which rotate 750 times per mile, it is impossible to measure
the distance to the thousanth of a mile so that last digit
is suspect for sure. There is no way to measure your distance
more accurately than within 85 inches or so.

Anyways, from the numbers you give is seems you meter is
"accurate." What is causing you discomfort is a lack of
"precision."

How's that for pedantic.

tcmedara said:

Forgot I'd sent a post off to Cateye regarding the time, distance, and ave
speed mismatches on my Enduro 2 cyclocomputer (or "bull skirt" as S o r n i
calls it).

Got the response today. For those who care:

Quoted message said:

Hi Tom

It has to do with how frequently the unit updates the information it is

receiving. For instance, current speed may be updated every x seconds, where
as the >calculation for average speed may be performed every y seconds. I
believe the calculation for current is performed much more frequently than
that for average, >hence this discrepancy. This, in effect, would make the
current speed data marginally more accurate that the average speed data, but
they are both pretty reliable.

Quoted message said:

(snip ID info)

Quoted message said:

Thanks for supporting Cat Eye!!!"

Interesting. I would have thought it was a pretty continuous process.

Basically there is something particular about the way Cateye does the
computations. Apparently their methodolgy has persisted for awhile:

http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&c2coff=1&q=Math+Errors+Bike+Computers&btnG=Search&meta=group%3Drec.bicycles.tech

Regarding the division problem posed by r = d/t, I wonder if any of these
computers can do much more than divide-by-two, since divide-by-two is a simple
bit shift operation.

On 28 Sep 2004 17:03:05 -0700, [email hidden]

Quoted message said:

Quoted message said:

Diablo Scott said:

[email hidden] wrote:

> Later today, I plan to see how well the Fury RoadMaster's
> new Schwinn speedometer does for roughly 4 miles and just
> under 13 minutes.
>
> Carl Fogel

Maybe try to estimate the average speed recalc rate as well. I

agree

Quoted message said:

Quoted message said:

it's probably every few seconds, rather than every thirty.

Dear Diablo,

I set the Schwinn speedometer to show average and set off.

Judging by my muttered count as the average changed, it's
updated roughly every 10 seconds--no reading at all for the
first ten seconds and then large jumps every ensuing ten
seconds to around 17 mph, at which point progress slowed
noticeably.

There were no interruptions, so once the Fury RoadMaster was
up to crusing speed, it was just a matter of cursing the
wind and the slight rise to the backstretch behind the zoo.

Eventually, the average reading exceeded 19 mph and the
little +/- indicating whether I was over or under began
chiding me now and then, as if I couldn't see the
speedometer dropping every so often.

At the end of the ride, the clock showed 12:16, the
astonishing trip meter showed 4.015 miles, and the
cyclocomputer offered to bet me that I had averaged 19.7
mph.

To my horror, this seems inaccurate, since (4.015 mph x 3600
seconds/hour ) divided by 736 seconds is only 19.638 mph,
not 19.7 mph. (Another ten seconds or quarter-turn of the
front tire might have led to a more honest and believable
estimate.)

Well, first of all, 4.015 * 3600 / 736 is 19.64 NOT 19.638.
Second, assuming the Fury RoadMaster has normal sized wheels
which rotate 750 times per mile, it is impossible to measure
the distance to the thousanth of a mile so that last digit
is suspect for sure. There is no way to measure your distance
more accurately than within 85 inches or so.

Anyways, from the numbers you give is seems you meter is
"accurate." What is causing you discomfort is a lack of
"precision."

How's that for pedantic.

Dear Jim,

Well, for pedantic, it could stand improvement.

First, my calculator shows 19.638586. That's closer to
19.638 than it is to 19.400. You should have argued for
16.639.

Second, a thousandth of a mile is 5.28 feet, or a touch over
63 inches. The Fury's mighty front tire measures around 2080
mm, or just under 82 inches. A reasonable bit of internal
calculation and rounding gives it an accuracy to within a
thousandth of a mile, plus or minus a thousandth. No digital
readout can be any more accurate than that.

But relax--my discomfort is more histronic than real.

Carl Fogel

Quoted message said:

Anyways, from the numbers you give is seems you meter is
"accurate." What is causing you discomfort is a lack of
"precision."

How's that for pedantic.

Schooling Carl on pedantics is a bit like schooling Lance Armstrong on
climbing.

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $695 ti frame

gwhite said:

tcmedara said:

Forgot I'd sent a post off to Cateye regarding the time, distance, and ave
speed mismatches on my Enduro 2 cyclocomputer (or "bull skirt" as S o r n i
calls it).

Got the response today. For those who care:

Quoted message said:

Hi Tom

It has to do with how frequently the unit updates the information it is

receiving. For instance, current speed may be updated every x seconds, where
as the >calculation for average speed may be performed every y seconds. I
believe the calculation for current is performed much more frequently than
that for average, >hence this discrepancy. This, in effect, would make the
current speed data marginally more accurate that the average speed data, but
they are both pretty reliable.

Quoted message said:

(snip ID info)

Quoted message said:

Thanks for supporting Cat Eye!!!"

Interesting. I would have thought it was a pretty continuous process.

Basically there is something particular about the way Cateye does the
computations. Apparently their methodolgy has persisted for awhile:

http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&c2coff=1&q=Math+Errors+Bike+Computers&btnG=Search&meta=group%3Drec.bicycles.tech

Regarding the division problem posed by r = d/t, I wonder if any of these
computers can do much more than divide-by-two, since divide-by-two is a simple
bit shift operation.

Dear G.,

Aha!

The sordid truth comes out--almost ten years later, brave
men are still struggling against ools inadequate to give the
correct average speeds that we so desperately need!

I have my own reasons for being wary of a brand named
Cateye.

Long ago, I learned that if you want to see a freshly minted
ophthalmologist's eyes light up, you do not offer her roses
or perfume, but instead mention that another eye surgeon has
acquired a jar of cat eyes from the animal shelter and is
willing to share them for practice dissections. (Cat eyes
are prized because they're just about the right size and
more uniform than dog optics.)

Ghoulishly,

Carl Fogel

Quoted message said:

I set the Schwinn speedometer to show average and set off.

Judging by my muttered count as the average changed, it's
updated roughly every 10 seconds--no reading at all for the
first ten seconds and then large jumps every ensuing ten
seconds to around 17 mph, at which point progress slowed
noticeably.

I noted the performance of my own Cateye Mity2 on my commute home from
work this evening. The auto-on function started with the first sensing
of the magnet, and the stopwatch timed out about 1 second after
stopping. The average speed recalc interval seemed to be about 12-15
seconds.

Trip dist = 3.53 miles
Trip time = 12m43s (headwind, plus this is my converted mtb)
Avg speed = 16.6 (I calc 16.655 so I would have rounded up to 16.7 but
I will give my Cateye's algorithm an A+)

--
My Bike Blog:
http://diabloscott.blogspot.com/