Computer math

"tcmedara" wrote: (clip)how would the average speed not equate to distance
traveled in one hour of elapsed time?
^^^^^^^^^^^^^^
I can think of two possibilities, both rather unlikely:
1.) Your computer calculates a DISTANCE average, rather than a time
average.
2. If you stop, your computer continues to record and display elapsed time
from the start of the ride, but takes time out for computing the average.

"tcmedara" <[email hidden]> wrote in news:KMp3d.203740$4o.74833
@fed1read01:

Quoted message said:

I know these aren't the most precise instruments in the world, but this one
struck me as odd. Given that the only two data points for the computer are
elapsed time and distance (as computed by distance/wheel rotation), how
would the average speed not equate to distance traveled in one hour of
elapsed time?

Many computers record both elapsed time (total clock time) and ride time (not
counting time when the wheels are not moving). The average speed uses the
latter time.

Ken said:

"tcmedara" <[email hidden]> wrote in news:KMp3d.203740$4o.74833
@fed1read01:

Quoted message said:

I know these aren't the most precise instruments in the world, but this one
struck me as odd. Given that the only two data points for the computer are
elapsed time and distance (as computed by distance/wheel rotation), how
would the average speed not equate to distance traveled in one hour of
elapsed time?

Many computers record both elapsed time (total clock time) and ride time (not
counting time when the wheels are not moving). The average speed uses the
latter time.

Howdy,

Assuming that you are correct, would that not cause the calculated
average MPH to be lower than 5 MPH in this example?

Thanks,

--
Kenneth

If you email... Please remove the "SPAMLESS."

Ken said:

"tcmedara" <[email hidden]> wrote in
news:KMp3d.203740$4o.74833 @fed1read01:

Quoted message said:

I know these aren't the most precise instruments in the world, but
this one struck me as odd. Given that the only two data points for
the computer are elapsed time and distance (as computed by
distance/wheel rotation), how would the average speed not equate to
distance traveled in one hour of elapsed time?

Many computers record both elapsed time (total clock time) and ride
time (not counting time when the wheels are not moving). The average
speed uses the latter time.

My understanding was that the time display on the Enduro 2 displayed actual
ride time (vice elapsed time, my error), i.e. time added only when the
sensor is picking up wheel rotations. As I was riding with my 10 year old,
there were several stops along the way. Total time (as read on the watch)
was well over an hour by the time the computer showed 1:00.

Obviously there's something I'm missing here. If this intelligent lot can't
figger it out, I might just have to email Cateye and get the company
approved reasoning. ......Perhaps I should do that anyway and see how that
compares to the answers here in RBT, eh?

Tom

tcmedara said:

Took the boy wonder out for an off-road adventure ride today. As I trailed
along somewhat bored watching boy wonder negotiate the trail ahead with the
speed of an overly cautious 10 year old, I started fiddling with my
computer.

Righ at the hour mark I managed to flip through the Cateye Endro 2's
functions and noted:
Time: 1:00
Distance 5.00 miles
Ave: 5.2 mph *<-----------???????*

I know these aren't the most precise instruments in the world, but this one
struck me as odd. Given that the only two data points for the computer are
elapsed time and distance (as computed by distance/wheel rotation), how
would the average speed not equate to distance traveled in one hour of
elapsed time?

Tom

And I bet you kept that average speed till the time registered 1 hour
2 minutes and 24 seconds.

Quoted message said:

tcmedara said:

Took the boy wonder out for an off-road adventure ride today. As I
trailed along somewhat bored watching boy wonder negotiate the trail
ahead with the speed of an overly cautious 10 year old, I started
fiddling with my computer.

Righ at the hour mark I managed to flip through the Cateye Endro 2's
functions and noted:
Time: 1:00
Distance 5.00 miles
Ave: 5.2 mph *<-----------???????*

I know these aren't the most precise instruments in the world, but
this one struck me as odd. Given that the only two data points for
the computer are elapsed time and distance (as computed by
distance/wheel rotation), how would the average speed not equate to
distance traveled in one hour of elapsed time?

Tom

And I bet you kept that average speed till the time registered 1 hour
2 minutes and 24 seconds.

Hmm, didn't think to check. If that were the case, then I guess you're
saying that the average computation is only performed every few minutes
rather than a continuous display of distance over time. I guess that could
be the case, though I seem to recall a much greater rate of change on the
ave display during the early part of several rides. I can't dispute your
suggestion -- I'll have to check it out next time I ride (and remember to
look....I normally don't obsess on the computer, just keep track of
distance). I did email Cateye just out of curiosity. I'll post their
response when I get it.

Topm

tcmedara said:

Took the boy wonder out for an off-road adventure ride today. As I trailed
along somewhat bored watching boy wonder negotiate the trail ahead with the
speed of an overly cautious 10 year old, I started fiddling with my
computer.

Righ at the hour mark I managed to flip through the Cateye Endro 2's
functions and noted:
Time: 1:00
Distance 5.00 miles
Ave: 5.2 mph *<-----------???????*

I know these aren't the most precise instruments in the world, but this one
struck me as odd. Given that the only two data points for the computer are
elapsed time and distance (as computed by distance/wheel rotation), how
would the average speed not equate to distance traveled in one hour of
elapsed time?

Tom

Dear Tom,

If your external figures show 1:00 hours, 5.00 miles, and
5.2 mph average time, then you need:

a) a badly programmed speedometer, or . . .

b) an internal distance of 5.2 miles (unlikely), or . . .

c) an internal time around 3462 seconds (138 seconds less
than a full hour), or . . .

d) an "average" that skips certain periods, or . . .

e) a speedometer that reads in odd-looking increments such
as 4.7, 5.2, 5.8, 6.3,6.9, and so forth (that is, a speedo
whose average-speed function will show only odd-looking
roughly half-mph points

f) a more accurate speedo that reads in tenths of an
mph--4.9, 5.0, 5.1, 5.2--but which still rounds up or down
along with c), a hidden internal time being slightly
different

I expect that the real answer will be g) something that
doesn't occur to me, but you might look into e) and see if
your speedometer reads 5.0, 5.1, 5.2, and so forth by
spinning the wheel and watching the numbers. If it switches
from 5.2 to 4.8, you've probably found the answer.

Carl Fogel

Quoted message said:

I expect that the real answer will be g) something that
doesn't occur to me, but you might look into e) and see if
your speedometer reads 5.0, 5.1, 5.2, and so forth by
spinning the wheel and watching the numbers. If it switches
from 5.2 to 4.8, you've probably found the answer.

Carl Fogel

Bike is on the stand right now. I'm going to now have to leave my cozy
computer chair and meander out to the garage in the interest of science.
Perhaps I'll just forget about it and get one of these!

http://www.schwinnbike.com/products/accessories_detail.php?id=53

If it's good enough for the likes of a tried and true racing bike, then
surely it won't be out of place on my generic, mass produced, cookie cutter
mountain bike..

Tom

"Kenneth" wrote: Assuming that you are correct, would that not cause the
calculated average MPH to be lower than 5 MPH in this example
^^^^^^^^^^^^^^^^
No, say you stopped riding for a couple minutes during the ride, so the
total elapsed time was 1 hour, but the time spent moving was, say, 58
minutes. 5 miles in 58 minutes is 5.17 MPH.

tcmedara said:

Took the boy wonder out for an off-road adventure ride today. As I
trailed along somewhat bored watching boy wonder negotiate the trail
ahead with the speed of an overly cautious 10 year old, I started
fiddling with my computer.

Righ at the hour mark I managed to flip through the Cateye Endro 2's
functions and noted:
Time: 1:00
Distance 5.00 miles
Ave: 5.2 mph *<-----------???????*

I know these aren't the most precise instruments in the world, but
this one struck me as odd. Given that the only two data points for
the computer are elapsed time and distance (as computed by
distance/wheel rotation), how would the average speed not equate to
distance traveled in one hour of elapsed time?

That's what you get for putting a cyclometer on a mountain bike.

Bill "like a skirt on a bull" S.

tcmedara said:

Quoted message said:

I expect that the real answer will be g) something that
doesn't occur to me, but you might look into e) and see if
your speedometer reads 5.0, 5.1, 5.2, and so forth by
spinning the wheel and watching the numbers. If it switches
from 5.2 to 4.8, you've probably found the answer.

Carl Fogel

Bike is on the stand right now. I'm going to now have to leave my cozy
computer chair and meander out to the garage in the interest of science.
Perhaps I'll just forget about it and get one of these!

http://www.schwinnbike.com/products/accessories_detail.php?id=53

If it's good enough for the likes of a tried and true racing bike, then
surely it won't be out of place on my generic, mass produced, cookie cutter
mountain bike..

Tom

Dear Tom,

Hmmm . . . odd, but that's a one-touch Schwinn 12-function
speedometer.

I can't find the two-button model sold at WalMart on
www.schwinn.com or at the WalMart site.

But either model probably works well enough.

Carl Fogel

tcmedara said:

Ken said:

"tcmedara" <[email hidden]> wrote in
news:KMp3d.203740$4o.74833 @fed1read01:

Quoted message said:

I know these aren't the most precise instruments in the world, but
this one struck me as odd. Given that the only two data points for
the computer are elapsed time and distance (as computed by
distance/wheel rotation), how would the average speed not equate to
distance traveled in one hour of elapsed time?

Many computers record both elapsed time (total clock time) and ride
time (not counting time when the wheels are not moving). The average
speed uses the latter time.

My understanding was that the time display on the Enduro 2 displayed actual
ride time (vice elapsed time, my error), i.e. time added only when the
sensor is picking up wheel rotations. As I was riding with my 10 year old,
there were several stops along the way. Total time (as read on the watch)
was well over an hour by the time the computer showed 1:00.

Obviously there's something I'm missing here. If this intelligent lot can't
figger it out, I might just have to email Cateye and get the company
approved reasoning. ......Perhaps I should do that anyway and see how that
compares to the answers here in RBT, eh?

Tom

I think the problem comes from a low-precision divide operation and
not-too-frequent updating of average speed. Cateye Enduro 2/Mity 3
computers use a 4-bit micro, probably running at a very low clock
speed to save power in order to give good battery life. It's not
that you can't get good precision from a 4-bit micro, but the higher
the precision and the more frequent the update, the more its little
brain is taxed. I've seen average-speed fluctuations on my Mity 3
that must be due to roundoff or truncation error, such as when
riding above the average speed (and so the average should not
decrease), but the display will go through some cycles of decreased
displayed average speed before showing an increased average speed.

Dave Lehnen

"S o r n i" <[email hidden]> wrote in message news:<[email hidden]>...

Quoted message said:

tcmedara said:

Took the boy wonder out for an off-road adventure ride today. As I
trailed along somewhat bored watching boy wonder negotiate the trail
ahead with the speed of an overly cautious 10 year old, I started
fiddling with my computer.

I imagine your Cateye works fine. Read the instructions. They explain
it very well. If you can't find the instructions, look em up on line
at "cateye"

Good luck, John

Leo Lichtman said:

No, say you stopped riding for a couple minutes during the ride, so the
total elapsed time was 1 hour, but the time spent moving was, say, 58
minutes. 5 miles in 58 minutes is 5.17 MPH.

Good that someone mentioned that. If your computer is set on "auto",
meaning that it stops counting when you stop, then it will adjust the
average speed accordingly. This was a response to complaints about the
average speed seeming too low. But it is not so clear that the
elapsed-time clock will also stop as readily. it might be programmed only
to stop after a certain amount of inactivity, rather than when the speed
drops below ~2mph.

--

David L. Johnson

__o | Some people used to claim that, if enough monkeys sat in front
_`\(,_ | of enough typewriters and typed long enough, eventually one of
(_)/ (_) | them would reproduce the collected works of Shakespeare. The
internet has proven this not to be the case.

John McGraw said:

"S o r n i" <[email hidden]> wrote in message
news:<[email hidden]>...

Quoted message said:

tcmedara said:

Took the boy wonder out for an off-road adventure ride today. As I
trailed along somewhat bored watching boy wonder negotiate the trail
ahead with the speed of an overly cautious 10 year old, I started
fiddling with my computer.

I imagine your Cateye works fine. Read the instructions. They explain
it very well. If you can't find the instructions, look em up on line
at "cateye"

Good luck, John

It seems to work well enough for my uses ("skirt on a bull" and all that), I
was merely curious. I read through the instructions and didn't find much by
way of explaination. The instruction sheet does say average speed is ±0.3
mph. Obviously my readings were well within that range, but it begs the
question. How is the figure derived if the only two data points are
distance and time? The average is not a direct measurement so it must be
derived from the data available to the machine and then go through some sort
of calculation. In this case the calculation itself introduced the error.
Bizarre events for my analog brain!

I'll go with Dave Lehnen's response elsewhere in the thread. Essentially:
low budget performance for a low budget computer. That I can grasp.

Tom

"tcmedara" <[email hidden]> wrote in message news:<m4L3d.3033$%t3.1720@lakeread01>...

Quoted message said:

John McGraw said:

"S o r n i" <[email hidden]> wrote in message
news:<[email hidden]>...

Quoted message said:

tcmedara wrote:
> Took the boy wonder out for an off-road adventure ride today. As I
> trailed along somewhat bored watching boy wonder negotiate the trail
> ahead with the speed of an overly cautious 10 year old, I started
> fiddling with my computer.
>

I imagine your Cateye works fine. Read the instructions. They explain
it very well. If you can't find the instructions, look em up on line
at "cateye"

Good luck, John

It seems to work well enough for my uses ("skirt on a bull" and all that), I
was merely curious. I read through the instructions and didn't find much by
way of explaination. The instruction sheet does say average speed is ±0.3
mph. Obviously my readings were well within that range, but it begs the
question. How is the figure derived if the only two data points are
distance and time? The average is not a direct measurement so it must be
derived from the data available to the machine and then go through some sort
of calculation. In this case the calculation itself introduced the error.
Bizarre events for my analog brain!

I'll go with Dave Lehnen's response elsewhere in the thread. Essentially:
low budget performance for a low budget computer. That I can grasp.

Tom

Sorry, I must have missed something. I'll reread the thread. It's
always made sense to me, but then maybe I've been blissfully ignorant.
For >15 yrs I've used Avocet's w/ the ring around the hub & have been
astounded by their accuracy. But recently I've had some physical
problems w/ Avocets, & started using Cateyes. Perhaps I should check
the cateye accuracy.
John

On 21 Sep 2004 01:02:18 -0700, [email hidden] (John

McGraw) said:

"tcmedara" <[email hidden]> wrote in message news:<m4L3d.3033$%t3.1720@lakeread01>...

Quoted message said:

John McGraw said:

"S o r n i" <[email hidden]> wrote in message
news:<[email hidden]>...
> tcmedara wrote:
>> Took the boy wonder out for an off-road adventure ride today. As I
>> trailed along somewhat bored watching boy wonder negotiate the trail
>> ahead with the speed of an overly cautious 10 year old, I started
>> fiddling with my computer.
>>

I imagine your Cateye works fine. Read the instructions. They explain
it very well. If you can't find the instructions, look em up on line
at "cateye"

Good luck, John

It seems to work well enough for my uses ("skirt on a bull" and all that), I
was merely curious. I read through the instructions and didn't find much by
way of explaination. The instruction sheet does say average speed is ±0.3
mph. Obviously my readings were well within that range, but it begs the
question. How is the figure derived if the only two data points are
distance and time? The average is not a direct measurement so it must be
derived from the data available to the machine and then go through some sort
of calculation. In this case the calculation itself introduced the error.
Bizarre events for my analog brain!

I'll go with Dave Lehnen's response elsewhere in the thread. Essentially:
low budget performance for a low budget computer. That I can grasp.

Tom

Sorry, I must have missed something. I'll reread the thread. It's
always made sense to me, but then maybe I've been blissfully ignorant.
For >15 yrs I've used Avocet's w/ the ring around the hub & have been
astounded by their accuracy. But recently I've had some physical
problems w/ Avocets, & started using Cateyes. Perhaps I should check
the cateye accuracy.
John

Dear John,

Here's the problem from the original post:

Right at the hour mark I managed to flip through the Cateye
Endro 2's functions and noted:
Time: 1:00
Distance 5.00 miles
Ave: 5.2 mph *<-----------???????*

Given 60 minutes and 5.00 miles, the question is why is the
average calculated as 5.2 mph?

If it's any reassurance, the accuracy of individual
measurements is likely to be ridiculously precise. That is,
the wheel probably made enough turns at its calibration of
20xx mm per revolution to reach 5.00 miles instead of 5.01
or 4.99, and the clock probably measured 1:00 hours far more
precisely than plus or minus 60 seconds.

So the problem is likely

a) bad programming (oops!)

b) odd rounding (the average function reads only in
odd-looking steps such as 4.3 4.8, 5.2, 5.7)

c) the use of a different internal timer for averaging (the
1:00 is total time since the ride began, while the hidden
internal timer noted when the wheel paused here or there on
the ride and reads a little over 2 minutes lower)

Whatever the explanation, I for one will not sleep well
until I have more confidence in the instruments that tell me
the rate at which I'm having fun.

Carl Fogel

Quoted message said:

tcmedara said:

Quoted message said:

I expect that the real answer will be g) something that
doesn't occur to me, but you might look into e) and see if
your speedometer reads 5.0, 5.1, 5.2, and so forth by
spinning the wheel and watching the numbers. If it switches
from 5.2 to 4.8, you've probably found the answer.

Carl Fogel

Bike is on the stand right now. I'm going to now have to leave my cozy
computer chair and meander out to the garage in the interest of science.
Perhaps I'll just forget about it and get one of these!

http://www.schwinnbike.com/products/accessories_detail.php?id=53

If it's good enough for the likes of a tried and true racing bike, then
surely it won't be out of place on my generic, mass produced, cookie cutter
mountain bike..

Tom

Dear Tom,

Hmmm . . . odd, but that's a one-touch Schwinn 12-function
speedometer.

I can't find the two-button model sold at WalMart on
www.schwinn.com or at the WalMart site.

But either model probably works well enough.

Carl Fogel

I have two of the one-touch 12-functions, purchased in 2003 at MalWart
;-)
Cost under ten bucks and work a treat. I use one for its intended
purpose, cannibalized the bottom half of the other to interface a second
wheel-turns sensor with a little circuit I built (continuously computes
instantaneous speed and saves each reading in non-volatile storage,
EEPROM, for later download).

Last week I went back to my MalWart to buy a couple more of this dandy
computer, but no joy; they no longer carry it. They do carry a
different though similar Schwinn computer.

Michael

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

Quoted message said:

On 21 Sep 2004 01:02:18 -0700, [email hidden] (John

McGraw) said:

"tcmedara" <[email hidden]> wrote in message news:<m4L3d.3033$%t3.1720@lakeread01>...

Quoted message said:

John McGraw <[email hidden]> wrote:
> "S o r n i" <[email hidden]> wrote in message
> news:<[email hidden]>...
>> tcmedara wrote:
>>> Took the boy wonder out for an off-road adventure ride today. As I
>>> trailed along somewhat bored watching boy wonder negotiate the trail
>>> ahead with the speed of an overly cautious 10 year old, I started
>>> fiddling with my computer.
>>>
>
> I imagine your Cateye works fine. Read the instructions. They explain
> it very well. If you can't find the instructions, look em up on line
> at "cateye"
>
> Good luck, John

It seems to work well enough for my uses ("skirt on a bull" and all that), I
was merely curious. I read through the instructions and didn't find much by
way of explaination. The instruction sheet does say average speed is ±0.3
mph. Obviously my readings were well within that range, but it begs the
question. How is the figure derived if the only two data points are
distance and time? The average is not a direct measurement so it must be
derived from the data available to the machine and then go through some sort
of calculation. In this case the calculation itself introduced the error.
Bizarre events for my analog brain!

I'll go with Dave Lehnen's response elsewhere in the thread. Essentially:
low budget performance for a low budget computer. That I can grasp.

Tom

Sorry, I must have missed something. I'll reread the thread. It's
always made sense to me, but then maybe I've been blissfully ignorant.
For >15 yrs I've used Avocet's w/ the ring around the hub & have been
astounded by their accuracy. But recently I've had some physical
problems w/ Avocets, & started using Cateyes. Perhaps I should check
the cateye accuracy.
John

Dear John,

Here's the problem from the original post:

Right at the hour mark I managed to flip through the Cateye
Endro 2's functions and noted:
Time: 1:00
Distance 5.00 miles
Ave: 5.2 mph *<-----------???????*

Given 60 minutes and 5.00 miles, the question is why is the
average calculated as 5.2 mph?

If it's any reassurance, the accuracy of individual
measurements is likely to be ridiculously precise. That is,
the wheel probably made enough turns at its calibration of
20xx mm per revolution to reach 5.00 miles instead of 5.01
or 4.99, and the clock probably measured 1:00 hours far more
precisely than plus or minus 60 seconds.

So the problem is likely

a) bad programming (oops!)

b) odd rounding (the average function reads only in
odd-looking steps such as 4.3 4.8, 5.2, 5.7)

c) the use of a different internal timer for averaging (the
1:00 is total time since the ride began, while the hidden
internal timer noted when the wheel paused here or there on
the ride and reads a little over 2 minutes lower)

Whatever the explanation, I for one will not sleep well
until I have more confidence in the instruments that tell me
the rate at which I'm having fun.

Carl Fogel

I thought that the OP was probably aware that, now a days, most
cyclometers stop recording time for average speed when the speed drops
below a set speed. Usually ~2mph. Did the OP stop for a few seconds
during his ride? that would account for it, if the time on the ride
timer doesn't stop, & the average speed does.
Best, John