Polar625x initial accuracy.

[email protected] wrote:
> I found that my initial accuracy was way off. I need to set on
> 800(80%) to make it accurate. Polar says most people have an initial
> accuracy around 97%.
> I am curious on what other people encountered with the 625x?
>
> Also, wonder why mine was so far off?
>
> Thanks for any respones.
>

I have used my 625 uncalibrated while running on hard-packed snow (not
too different from dirt) on trails. In a couple months when I can run on
gravel along a section-line road, I'll be able to calibrate it - unless
I'm afraid of messing it up. (it arrived during 1st snow). Even my
initial runs in snowy, slippery slop looked like they were within 10%.
But my experience (see details below) is consistent with it being 97%
accurate on simple terrain with no calibration.

Did you run a known distance uncalibrated to see now close it was before
you tried to calibrate? How repeatable were your measurements -
uncalibrated, calibrated? That is, did you get random numbers when
running the same route or were the numbers similar? Did you try just
running with it without going into calibration mode?

Is it firmly anchored on your shoestrings? I was initially using mine on
one pair of shoes with nylon laces and it fit really snugly. I'm now
using it on shoe with cotton laces (otherwise, same model) (laces are
there from an experiment and need to replace them with the nylon, but
haven't gotten around to it yet). Since the cotton seems to flatten as
it's tightened, it doesn't hold the footpod as snugly.

Do you have a short foot that the flexion might be affecting the pod's
position? Are there unit inconsistencies - ft, m, km, mi - although I'm
having trouble finding where 80% might work in there. Just pulling at
straws.


(I just snipped this from end of recent post on hrm recommendations)

For simple terrain, it seems to be within about 3% of my best
guesstimate of overall distance - out of the box. For some trails, I've
had either a map with "measured" (not sure exact methods, but reported
in 1-m increments) distances between intersections or some mile posts
(clueless as to accuracy but they're at start of Iditarod Trail). For
other trails I may just have a route on map or a gps distance. At any
rate, for most conditions for total distance, values are within about 3%
of each other most of the time - occasionally out to 5%, many times
within 0-1% of alternate best guess. I've found it really handy for the
ice we've had the last few weeks when I've just been running laps up and
back in a mowed hay field (grass covers ice) - distances on each lap
were reasonably repeatable, given I may not have been running exactly
the same place. I also ended up with a little bushwhacking in a
snowstorm (don't ask) with it the other evening, with reasonable
results. Its distance estimates are close enough to any other estimate
that I have, that I just use it now for running.

Not sure how it will do on our regular hills (10-30%) when I have a good
surface, but suspect it will be off there - but may cancel out by the
time I go up and down.

I haven't used it on twisty single track yet. I don't think I had good
results on loose snow on 20%+ slope, but I didn't have any real results
to compare it to. It was 1/2 step back for each step up, and a
landmarkless location where I turned around.

Dot

--
"You try to slow down and enjoy it. You try to look at the scenery. But
your brain can kind of go blank. All you want to do is tell your feet to
keep working."
-Cedar Petrosius, women's winner 2004 Matanuska Peak Challenge (14mi,
9000ft up and down)

Thanks for the info and your experiences. I have a size 10 foot and
use nylon laces. Your point about being tight is interesting. I will
make sure it is snug on the shoe, but i believe it is. The results it
gets are pretty consistent. That is same route, same mileage.
I have checked it against known distances(bike computer). And have
used a GPS unit(forerunner) along with it several times. When
comparing to the GPS unit, it tends to register a little different
going up/down hill than on the flats. That is, on the flats it gains a
little and up/down hill looses a little. But that has not been
verified too much. And this is when the setting is 80%. At
100%(factory setting) it is way off. Makes me a much faster runner.
My running is mix of payment/gravel roads. Have not tried on Trail
yet.

I guess i just have a stride or something that makes it further off for
me. I have pretty long legs and have a long stride. Wonder if that
has anything to do with it.
The foot pod technology was developed by a company called Dynastream.
Here is an interesting link to a paper discussing the technology.
http://www.dynastream.com/datafiles/SpeedMax White Paper v4_1.pdf

Another interesting thing about that foot pod. I checked on buying an
extra from Polar. $125 Expensive little piece of equipment! Your
caution about not wanting to ruin it is well founded,
Duane

[email protected] wrote:

> Thanks for the info and your experiences. I have a size 10 foot

Should be plenty large. I'm 8.5 women's.

and
> use nylon laces. Your point about being tight is interesting. I will
> make sure it is snug on the shoe, but i believe it is. The results it
> gets are pretty consistent.

That is interesting - repeatable, but inaccurate. OTOH, if the
calibration makes it accurate then it shouldn't be an issue.


That is same route, same mileage.
> I have checked it against known distances(bike computer). And have
> used a GPS unit(forerunner) along with it several times. When
> comparing to the GPS unit, it tends to register a little different
> going up/down hill than on the flats. That is, on the flats it gains a
> little and up/down hill looses a little.

One of my routes has a map with distances between intersections to 1-m
(can't remember the method they used, but I've been told they've been
measured a couple times), and I was hitting most of the distances almost
right on (within 0-1%) - except for the 2 stretches with small gentle
hills (maybe 3-5% there, iirc). IIRC, the downhill estimate was short
and uphill long - consistent with longer strides on down and shorter on
up. But when all was said and done, the total mileage was consistent
with other estimates, which is my main concern. Distance between
intersections varies from about 100m to < 600 m, so I could keep close
tabs on distances. I was surprised how close it came to my estimates the
other night where I was bushwhacking in some fresh snow on top lumpy
(tussocky) ground, so stride was almost meaningless - but it was
relatively flat in that area.

I run by time predominantly, but like to have a reasonable estimate of
distance and elevation change to check progress toward TOL for event
goals, so it's working quite well for me - although not as useful as gps
with a decent signal (snowshoe, xc ski, bike, etc). After the snow goes
out, I'll try it on one of the local mountains to check about hills, and
calibrate it on flat gravel area. The snow on it is too loose right now
to make meaningful steps.


But that has not been
> verified too much. And this is when the setting is 80%. At
> 100%(factory setting) it is way off. Makes me a much faster runner.
> My running is mix of payment/gravel roads. Have not tried on Trail
> yet.
>
> I guess i just have a stride or something that makes it further off for
> me. I have pretty long legs and have a long stride. Wonder if that
> has anything to do with it.

Could be. However, if the device is truly sensing by motion, it
shouldn't matter. However, there's probably some assumptions in their
default settings.


> The foot pod technology was developed by a company called Dynastream.
> Here is an interesting link to a paper discussing the technology.
> http://www.dynastream.com/datafiles/SpeedMax White Paper v4_1.pdf

Thanks. Yes, after Anders posted about the announcement of the 625 last
year (day after I put in for a 720 in a group purchase, which I promptly
cancelled), I was impressed enough with the technology that I thought it
worthwhile waiting for it when I was going to upgrade.

>
> Another interesting thing about that foot pod. I checked on buying an
> extra from Polar. $125 Expensive little piece of equipment! Your
> caution about not wanting to ruin it is well founded,

It's supposed to be waterproof, but for awhile there, my footing so
awful because of the slush, that it didn't make sense to try it, and it
seemed to be rubbing my feet a little. And it didn't do well on
snowshoes on my one test either, but that was also really soft snow.
After things dried out and firmed up, I got curious and couldn't wait
til snow-free surface was available, so have tested it running on snow
I haven't retried it with snowshoes since we haven't had that much
good snow.

Dot

--
"You try to slow down and enjoy it. You try to look at the scenery. But
your brain can kind of go blank. All you want to do is tell your feet to
keep working."
-Cedar Petrosius, women's winner 2004 Matanuska Peak Challenge (14mi,
9000ft up and down)