I have posted this discussion before but it still bugs me. Today I ride 64 miles on some rolling hills but nothing considered climbing. My Garmin 935 has elevation gain 1263. RIde withe the GPS says I did 1639 feet of climbing. I would think that is based on terrain that they have in maps and data and pretty accurate. My 935 does has barometric altimeter but would that be more accurate? No matter what ride I do there is always a difference with a error rate around 25%. That seems alot to me.
Deacon Mark

On Thursday, June 30, 2022 at 10:19:39 PM UTC+2, deaco...@gmail.com wrote:
> I have posted this discussion before but it still bugs me. Today I ride 64 miles on some rolling hills but nothing considered climbing. My Garmin 935 has elevation gain 1263. RIde withe the GPS says I did 1639 feet of climbing. I would think that is based on terrain that they have in maps and data and pretty accurate. My 935 does has barometric altimeter but would that be more accurate? No matter what ride I do there is always a difference with a error rate around 25%. That seems alot to me.
> Deacon Mark

How was the weather? Stable? If Yes, trust your Garmin.

Lou

On Thursday, June 30, 2022 at 2:10:28 PM UTC-7, Lou Holtman wrote:
> On Thursday, June 30, 2022 at 10:19:39 PM UTC+2, deaco...@gmail.com wrote:
> > I have posted this discussion before but it still bugs me. Today I ride 64 miles on some rolling hills but nothing considered climbing. My Garmin 935 has elevation gain 1263. RIde withe the GPS says I did 1639 feet of climbing. I would think that is based on terrain that they have in maps and data and pretty accurate. My 935 does has barometric altimeter but would that be more accurate? No matter what ride I do there is always a difference with a error rate around 25%. That seems alot to me.
> > Deacon Mark
> How was the weather? Stable? If Yes, trust your Garmin.

I'm not real sure of that. My grade seems to move very slowly and i would expect a fairly large error. But since I haven't been doing any climbs for the last 6 weeks I really have nothing to base that on. Perhaps it has a large delay in the gradient but the altitude reads accurately. On one of my climbing rides, there is a spot that is 900 feet and another that is 1100 feet so that I can compare. The 1100 is followed by a descent followed by another steep climb that I have never successfully measured since getting to the top of that always has be burned out.

Tom Kunich <cyclintom@gmail.com> wrote:
> On Thursday, June 30, 2022 at 2:10:28 PM UTC-7, Lou Holtman wrote:
>> On Thursday, June 30, 2022 at 10:19:39 PM UTC+2, deaco...@gmail.com wrote:
>>> I have posted this discussion before but it still bugs me. Today I ride
>>> 64 miles on some rolling hills but nothing considered climbing. My
>>> Garmin 935 has elevation gain 1263. RIde withe the GPS says I did 1639
>>> feet of climbing. I would think that is based on terrain that they have
>>> in maps and data and pretty accurate. My 935 does has barometric
>>> altimeter but would that be more accurate? No matter what ride I do
>>> there is always a difference with a error rate around 25%. That seems alot to me.
>>> Deacon Mark
>> How was the weather? Stable? If Yes, trust your Garmin.
>
> I'm not real sure of that. My grade seems to move very slowly and i would
> expect a fairly large error. But since I haven't been doing any climbs
> for the last 6 weeks I really have nothing to base that on. Perhaps it
> has a large delay in the gradient but the altitude reads accurately. On
> one of my climbing rides, there is a spot that is 900 feet and another
> that is 1100 feet so that I can compare. The 1100 is followed by a
> descent followed by another steep climb that I have never successfully
> measured since getting to the top of that always has be burned out.
>

My Garmin 830 + Garmin connect/Strava give exactly same figures it should
be fairly close.

Roger Merriman

Mark Cleary <deaconmjc08@gmail.com> wrote:
> I have posted this discussion before but it still bugs me. Today I ride
> 64 miles on some rolling hills but nothing considered climbing. My Garmin
> 935 has elevation gain 1263. RIde withe the GPS says I did 1639 feet of
> climbing. I would think that is based on terrain that they have in maps
> and data and pretty accurate. My 935 does has barometric altimeter but
> would that be more accurate? No matter what ride I do there is always a
> difference with a error rate around 25%. That seems alot to me.
> Deacon Mark
>

I think that Garmins tend to ignore slight changes in elevation and very
small slopes, so I would always assume the Garmin would read low.

On Thu, 30 Jun 2022 13:19:36 -0700 (PDT), Mark Cleary
<deaconmjc08@gmail.com> wrote:

>I have posted this discussion before but it still bugs me. Today I ride 64 miles on some rolling hills but nothing considered climbing. My Garmin 935 has elevation gain 1263. RIde withe the GPS says I did 1639 feet of climbing. I would think that is based on terrain that they have in maps and data and pretty accurate. My 935 does has barometric altimeter but would that be more accurate? No matter what ride I do there is always a difference with a error rate around 25%. That seems alot to me.
>Deacon Mark

Did you calibrate the MEMS barometric pressure sensor? If you let it
calibrate itself using GPS, you'll get 8 times worse accuracy than if
you calibrate it manually at the start of each ride.

"The Elevation Reading on My Forerunner 935 Is Wrong"
<https://support.garmin.com/en-US/?faq=fFqaolJqep3QqZY5UqOCa6&productID=564291&tab=topics>
"With proper calibration, the watch can achieve an accuracy of +/-50
feet.

Auto Cal. - When enabled this option will calibrate the altimeter
anytime GPS is acquired.

Calibrate - This mode will allow you to calibrate the sensor using
a current known elevation or the GPS elevation reading. Elevation
calibrated through GPS is accurate to +/-400 feet."

"Understanding the Accuracy of the GPS Elevation Reading"
<https://support.garmin.com/en-US/?faq=QPc5x3ZFUv1QyoxITW2vZ6>
"It is not uncommon for satellite heights to be off from map
elevations by +/- 400 ft."

Elevation from GPS is less accurate than 2D position accuracy. A
simplified explanation of this is that in order to determine
elevation, the GPS birds need to be moving either toward or away from
your GPS receiver. GPS birds fly at an altitude of 20,200 km. As
seen from the ground, the vertical component of the Doppler shift in
the Z axis (up-down) is much less than the X and Y (E-W and N-S)
component. The X and Y coordinates are used to establish the location
or 2D position. The Z axis establishes the altitude, with the aid of
some spherical geometry that I don't want to explain. Suffice to say
that a smaller Doppler shift change results in less accuracy.

MEMS barometric pressure sensors are fairly good for measuring
relative elevation changes, but problematic for absolute elevation
measurements. To measure absolute elevation, these need a reference
altitude at the start of a ride (or some known point in between). As
I previously mumbled, GPS elevation accuracy isn't as accurate as 2D
position. Therefore, even with GPS calibration, the final barometric
elevation is the sum of the GPS and MEMS sensor errors. If you use a
know reference altitude to calibrate the barometric pressure sensor,
you eliminate the GPS elevation error, but add in map and survey
errors.

The construction of the MEMS barometric pressure sensor in the Garmin
935 also adds a few errors. Temperature, wind, position, vibration,
etc can have an effect on the sensor measurement. Obtaining an
accurate reading while bouncing down a trail is difficult. Response
time and sampling time for the sensor is also a problem. To prevent
wild swings in measured altitude, air enters and leaves the sensor
though tiny holes which act as a damper. There's probably also some
digital damping and averaging. Data is sampled at a slow interval
such as once every few seconds so as not to deplete the watch battery.
The result is a rather ugly lag in the elevation profile graph when
plotted and a delay in obtaining an accurate altitude reading. The
GPS watch does not have the benefit of stored maps, so it can't cheat
and just translate 2D position to map based elevation. Even if it
did, as in larger GPS cycling computers, the errors in 2D position
translate into huge errors in altitude when riding a road which is
carved out of the side of a hillside.

Hopefully, I've explained enough that you understand the problems
involved in obtaining an accurate measurement. I can fill in the
details later. Too much plumbing today.

--
Jeff Liebermann jeffl@cruzio.com
PO Box 272 http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann AE6KS 831-336-2558

Am Thu, 30 Jun 2022 13:19:36 -0700 (PDT) schrieb Mark Cleary
<deaconmjc08@gmail.com>:

>I have posted this discussion before but it still bugs me.
>Today I ride 64 miles on some rolling hills but nothing
>considered climbing. My Garmin 935 has elevation gain 1263.
>RIde withe the GPS says I did 1639 feet of climbing. I would
>think that is based on terrain that they have in maps and
>data and pretty accurate.

Elevation data (SRTM) isn't that precise, but so is GPS data wrt the z
coordinate, especially when you don't have free sight around you.
Barometric data has it's own problems: air pressure varies with time and
location. So it's good for getting the noise out of vertical GPS data,
but not taht usefull for getting absolute data. Devices like those from
Garmin try to integrate all that data, using some trivial and some
elaborated, but proprietary algoriths, do a good job at that. But
sometimes they fail.

Another point: there is noise in the data which is real. Do you expect a
speed bump to count as elevation, when computing cumulative gain? What
about a short hollow through which the wheel i.W. rolled through without
losing speed? Depending on who you are and what the purpose is, people
apply different kinds of smoothing to the elevation curve.

>My 935 does has barometric
>altimeter but would that be more accurate?

Yes.

>No matter what
>ride I do there is always a difference with a error rate
>around 25%. That seems alot to me.

What does that error rate mean, how is it computed?

--
Wir danken für die Beachtung aller Sicherheitsbestimmungen

Am 30.06.2022 um 23:10 schrieb Lou Holtman:
> On Thursday, June 30, 2022 at 10:19:39 PM UTC+2, deaco...@gmail.com
> wrote:
>> I have posted this discussion before but it still bugs me. Today I
>> ride 64 miles on some rolling hills but nothing considered
>> climbing. My Garmin 935 has elevation gain 1263. RIde withe the GPS
>> says I did 1639 feet of climbing. I would think that is based on
>> terrain that they have in maps and data and pretty accurate. My 935
>> does has barometric altimeter but would that be more accurate? No
>> matter what ride I do there is always a difference with a error
>> rate around 25%. That seems alot to me.

> How was the weather? Stable? If Yes, trust your Garmin.

I speculate that 'Ride with GPS' does not correct altitude errors in
GPS. I speculate that barometric altimeters err on measuring too much
rather than too little when the weather changes significantly.

If you were riding on roads rather than MTBing, I'd upload the GPS track
to Strava and trust the elevation gain stats given there.

Rolf

On Friday, July 1, 2022 at 12:22:45 PM UTC+2, Rolf Mantel wrote:
> Am 30.06.2022 um 23:10 schrieb Lou Holtman:
> > On Thursday, June 30, 2022 at 10:19:39 PM UTC+2, deaco...@gmail.com
> > wrote:
> >> I have posted this discussion before but it still bugs me. Today I
> >> ride 64 miles on some rolling hills but nothing considered
> >> climbing. My Garmin 935 has elevation gain 1263. RIde withe the GPS
> >> says I did 1639 feet of climbing. I would think that is based on
> >> terrain that they have in maps and data and pretty accurate. My 935
> >> does has barometric altimeter but would that be more accurate? No
> >> matter what ride I do there is always a difference with a error
> >> rate around 25%. That seems alot to me.
> > How was the weather? Stable? If Yes, trust your Garmin.
> I speculate that 'Ride with GPS' does not correct altitude errors in
> GPS. I speculate that barometric altimeters err on measuring too much
> rather than too little when the weather changes significantly.
>
> If you were riding on roads rather than MTBing, I'd upload the GPS track
> to Strava and trust the elevation gain stats given there.
>
> Rolf

Around here I don't pay much attention to the elevation gain because it is pancaake flat. Todays ride almost 85 km and Strava says 43 m elevation gain.. Pff. but in the big mountains (Alpes) the Garmin is dead on when the weather was stable; Strava reported most of the time too much elevation gain. The difference Mark saw was 376 feet, about 114 m. Nothing to get upset about. People expect too much accuracy. Friend of mine complained on the top of the Passo Stelvio (2760 m) that his Garmin was 50 meters off. WTF.

Lou

Rolf Mantel <news@hartig-mantel.de> wrote:
> Am 30.06.2022 um 23:10 schrieb Lou Holtman:
>> On Thursday, June 30, 2022 at 10:19:39 PM UTC+2, deaco...@gmail.com
>> wrote:
>>> I have posted this discussion before but it still bugs me. Today I
>>> ride 64 miles on some rolling hills but nothing considered
>>> climbing. My Garmin 935 has elevation gain 1263. RIde withe the GPS
>>> says I did 1639 feet of climbing. I would think that is based on
>>> terrain that they have in maps and data and pretty accurate. My 935
>>> does has barometric altimeter but would that be more accurate? No
>>> matter what ride I do there is always a difference with a error
>>> rate around 25%. That seems alot to me.
>
>> How was the weather? Stable? If Yes, trust your Garmin.
>
> I speculate that 'Ride with GPS' does not correct altitude errors in
> GPS. I speculate that barometric altimeters err on measuring too much
> rather than too little when the weather changes significantly.
>
> If you were riding on roads rather than MTBing, I'd upload the GPS track
> to Strava and trust the elevation gain stats given there.
>
> Rolf
>

I’ve only noticed it if the weather changes ie suddenly low pressure front
etc. even MTBing Strava and Garmin (830 so has barometric altimeter) is
generally the same figure.

I have if riding in said weather, seen that I’m riding below sea level for
example as it’s been thrown by the storm etc.

Though that’s unusual most of the time the height is generally believable.

Roger Merriman

On Friday, July 1, 2022 at 12:01:43 AM UTC-7, Wolfgang Strobl wrote:
> Am Thu, 30 Jun 2022 13:19:36 -0700 (PDT) schrieb Mark Cleary
> <deaco...@gmail.com>:
> >I have posted this discussion before but it still bugs me.
> >Today I ride 64 miles on some rolling hills but nothing
> >considered climbing. My Garmin 935 has elevation gain 1263.
> >RIde withe the GPS says I did 1639 feet of climbing. I would
> >think that is based on terrain that they have in maps and
> >data and pretty accurate.
> Elevation data (SRTM) isn't that precise, but so is GPS data wrt the z
> coordinate, especially when you don't have free sight around you.
> Barometric data has it's own problems: air pressure varies with time and
> location. So it's good for getting the noise out of vertical GPS data,
> but not taht usefull for getting absolute data. Devices like those from
> Garmin try to integrate all that data, using some trivial and some
> elaborated, but proprietary algoriths, do a good job at that. But
> sometimes they fail.
>
> Another point: there is noise in the data which is real. Do you expect a
> speed bump to count as elevation, when computing cumulative gain? What
> about a short hollow through which the wheel i.W. rolled through without
> losing speed? Depending on who you are and what the purpose is, people
> apply different kinds of smoothing to the elevation curve.
> >My 935 does has barometric
> >altimeter but would that be more accurate?
> Yes.
> >No matter what
> >ride I do there is always a difference with a error rate
> >around 25%. That seems alot to me.
> What does that error rate mean, how is it computed?
>
> --
> Wir danken für die Beachtung aller Sicherheitsbestimmungen

I would really like to know what calculation they are using for altitude gain. As for atmospheric pressure - that changes very slowly and when you turn a Garmin on it remembers home altitude and can correct for atmospheric pressure.

On Friday, July 1, 2022 at 6:56:54 AM UTC-7, Lou Holtman wrote:
> On Friday, July 1, 2022 at 12:22:45 PM UTC+2, Rolf Mantel wrote:
> > Am 30.06.2022 um 23:10 schrieb Lou Holtman:
> > > On Thursday, June 30, 2022 at 10:19:39 PM UTC+2, deaco...@gmail.com
> > > wrote:
> > >> I have posted this discussion before but it still bugs me. Today I
> > >> ride 64 miles on some rolling hills but nothing considered
> > >> climbing. My Garmin 935 has elevation gain 1263. RIde withe the GPS
> > >> says I did 1639 feet of climbing. I would think that is based on
> > >> terrain that they have in maps and data and pretty accurate. My 935
> > >> does has barometric altimeter but would that be more accurate? No
> > >> matter what ride I do there is always a difference with a error
> > >> rate around 25%. That seems alot to me.
> > > How was the weather? Stable? If Yes, trust your Garmin.
> > I speculate that 'Ride with GPS' does not correct altitude errors in
> > GPS. I speculate that barometric altimeters err on measuring too much
> > rather than too little when the weather changes significantly.
> >
> > If you were riding on roads rather than MTBing, I'd upload the GPS track
> > to Strava and trust the elevation gain stats given there.
> >
> > Rolf
> Around here I don't pay much attention to the elevation gain because it is pancaake flat. Todays ride almost 85 km and Strava says 43 m elevation gain. Pff. but in the big mountains (Alpes) the Garmin is dead on when the weather was stable; Strava reported most of the time too much elevation gain. The difference Mark saw was 376 feet, about 114 m. Nothing to get upset about. People expect too much accuracy. Friend of mine complained on the top of the Passo Stelvio (2760 m) that his Garmin was 50 meters off. WTF.

My Garmin is off in distance quite a way - 7% - so with variations that large, you certainly can't complain about 50 meters.

On 7/1/2022 1:23 AM, Jeff Liebermann wrote:
>
>
> MEMS barometric pressure sensors are fairly good for measuring
> relative elevation changes, but problematic for absolute elevation
> measurements. To measure absolute elevation, these need a reference
> altitude at the start of a ride (or some known point in between). As
> I previously mumbled, GPS elevation accuracy isn't as accurate as 2D
> position. Therefore, even with GPS calibration, the final barometric
> elevation is the sum of the GPS and MEMS sensor errors. If you use a
> know reference altitude to calibrate the barometric pressure sensor,
> you eliminate the GPS elevation error, but add in map and survey
> errors.
>
> The construction of the MEMS barometric pressure sensor in the Garmin
> 935 also adds a few errors. Temperature, wind, position, vibration,
> etc can have an effect on the sensor measurement. Obtaining an
> accurate reading while bouncing down a trail is difficult. Response
> time and sampling time for the sensor is also a problem. To prevent
> wild swings in measured altitude, air enters and leaves the sensor
> though tiny holes which act as a damper. There's probably also some
> digital damping and averaging. Data is sampled at a slow interval
> such as once every few seconds so as not to deplete the watch battery.
> The result is a rather ugly lag in the elevation profile graph when
> plotted and a delay in obtaining an accurate altitude reading.

I have a more basic problem. A quite nice Nike Lance Armstrong
wristwatch with compass and altimeter was given to me (back when Lance's
name was still a marketing benefit). But its altimeter long ago lost its
mind. When powered up, it claims continuous and rapid altitude gain.
Nike wanted a fortune to "fix" (probably replace) it many years ago.

I suppose I could fire it up, go for a bike ride and do some bragging
here about my climbing prowess...

--
- Frank Krygowski

Frank Krygowski <frkrygow@sbcglobal.net> wrote:
> On 7/1/2022 1:23 AM, Jeff Liebermann wrote:
>>
>>
>> MEMS barometric pressure sensors are fairly good for measuring
>> relative elevation changes, but problematic for absolute elevation
>> measurements. To measure absolute elevation, these need a reference
>> altitude at the start of a ride (or some known point in between). As
>> I previously mumbled, GPS elevation accuracy isn't as accurate as 2D
>> position. Therefore, even with GPS calibration, the final barometric
>> elevation is the sum of the GPS and MEMS sensor errors. If you use a
>> know reference altitude to calibrate the barometric pressure sensor,
>> you eliminate the GPS elevation error, but add in map and survey
>> errors.
>>
>> The construction of the MEMS barometric pressure sensor in the Garmin
>> 935 also adds a few errors. Temperature, wind, position, vibration,
>> etc can have an effect on the sensor measurement. Obtaining an
>> accurate reading while bouncing down a trail is difficult. Response
>> time and sampling time for the sensor is also a problem. To prevent
>> wild swings in measured altitude, air enters and leaves the sensor
>> though tiny holes which act as a damper. There's probably also some
>> digital damping and averaging. Data is sampled at a slow interval
>> such as once every few seconds so as not to deplete the watch battery.
>> The result is a rather ugly lag in the elevation profile graph when
>> plotted and a delay in obtaining an accurate altitude reading.
>
> I have a more basic problem. A quite nice Nike Lance Armstrong
> wristwatch with compass and altimeter was given to me (back when Lance's
> name was still a marketing benefit). But its altimeter long ago lost its
> mind. When powered up, it claims continuous and rapid altitude gain.
> Nike wanted a fortune to "fix" (probably replace) it many years ago.
>
> I suppose I could fire it up, go for a bike ride and do some bragging
> here about my climbing prowess...
>
>
Does it record a GPX file ie GPS trace if so Strava or similar should
correct the elevation.

Or simply not look at the elevation I guess!

Roger Merriman

On 7/1/2022 3:59 PM, Roger Merriman wrote:
> Frank Krygowski <frkrygow@sbcglobal.net> wrote:
>> On 7/1/2022 1:23 AM, Jeff Liebermann wrote:
>>>
>>>
>>> MEMS barometric pressure sensors are fairly good for measuring
>>> relative elevation changes, but problematic for absolute elevation
>>> measurements. To measure absolute elevation, these need a reference
>>> altitude at the start of a ride (or some known point in between). As
>>> I previously mumbled, GPS elevation accuracy isn't as accurate as 2D
>>> position. Therefore, even with GPS calibration, the final barometric
>>> elevation is the sum of the GPS and MEMS sensor errors. If you use a
>>> know reference altitude to calibrate the barometric pressure sensor,
>>> you eliminate the GPS elevation error, but add in map and survey
>>> errors.
>>>
>>> The construction of the MEMS barometric pressure sensor in the Garmin
>>> 935 also adds a few errors. Temperature, wind, position, vibration,
>>> etc can have an effect on the sensor measurement. Obtaining an
>>> accurate reading while bouncing down a trail is difficult. Response
>>> time and sampling time for the sensor is also a problem. To prevent
>>> wild swings in measured altitude, air enters and leaves the sensor
>>> though tiny holes which act as a damper. There's probably also some
>>> digital damping and averaging. Data is sampled at a slow interval
>>> such as once every few seconds so as not to deplete the watch battery.
>>> The result is a rather ugly lag in the elevation profile graph when
>>> plotted and a delay in obtaining an accurate altitude reading.
>>
>> I have a more basic problem. A quite nice Nike Lance Armstrong
>> wristwatch with compass and altimeter was given to me (back when Lance's
>> name was still a marketing benefit). But its altimeter long ago lost its
>> mind. When powered up, it claims continuous and rapid altitude gain.
>> Nike wanted a fortune to "fix" (probably replace) it many years ago.
>>
>> I suppose I could fire it up, go for a bike ride and do some bragging
>> here about my climbing prowess...
>>
>>
> Does it record a GPX file ie GPS trace if so Strava or similar should
> correct the elevation.

Nope. It's been without a battery for years, but IIRC it shows current
altitude and (optionally) a plot of altitude vs. time. Ditto for
barometric pressure vs. time, which is the same thing with adjustments.

The electronic compass was a bit of a disappointment as well. I recall
having to recalibrate it pretty often.

--
- Frank Krygowski

On Fri, 1 Jul 2022 14:29:21 -0400, Frank Krygowski
<frkrygow@sbcglobal.net> wrote:
(chomp)
>I have a more basic problem. A quite nice Nike Lance Armstrong
>wristwatch with compass and altimeter was given to me (back when Lance's
>name was still a marketing benefit).

Which one?
<https://www.google.com/search?q=lance+armstrong+watch+nike&tbm=isch>
<https://www.swisswatchexpo.com/TheWatchClub/2020/02/10/lance-armstrong-watches/>
Maker and model number if possible. If you still have the
documentation or box, they should the FCC ID number. I might need
that to determine the type of sensors it uses. Don't be surprised if
the altimeter/compass module and case are made by two different
companies, and sold by a third company.

MEMS sensors can be very fragile. I've read about MEMS sensors in
watches that were killed by sudden changes in air pressure.

>But its altimeter long ago lost its
>mind. When powered up, it claims continuous and rapid altitude gain.
>Nike wanted a fortune to "fix" (probably replace) it many years ago.

I've seen that on rarely recent MEMS sensors that use resistive
bridges.
<https://www.allaboutcircuits.com/news/rohms-waterproof-barometric-pressure-sensor-is-more-than-a-weather-forecaster/>
When one of the four bridge resistors goes open circuit, the bridge
becomes drastically unbalanced and shows a ridiculously high or low
altitude. That's only one type of sensor. If it were piezo-resistive
or piezo-electric, things fail differently. Incidentally, negative
altitudes are possible with this type of failure. I have some of the
necessary SMD tools necessary to do the repair, but lack a supplier
for a currently unspecified MEMS sensor.

>I suppose I could fire it up, go for a bike ride and do some bragging
>here about my climbing prowess...

You're making it difficult for me to be inspired.
--
Jeff Liebermann jeffl@cruzio.com
PO Box 272 http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann AE6KS 831-336-2558

On 7/1/2022 8:27 PM, Jeff Liebermann wrote:
> On Fri, 1 Jul 2022 14:29:21 -0400, Frank Krygowski
> <frkrygow@sbcglobal.net> wrote:
> (chomp)
>> I have a more basic problem. A quite nice Nike Lance Armstrong
>> wristwatch with compass and altimeter was given to me (back when Lance's
>> name was still a marketing benefit).
>
> Which one?
> <https://www.google.com/search?q=lance+armstrong+watch+nike&tbm=isch>

This one:
https://www.amazon.co.uk/Nike-WA0020-013-Lance-Armstrong-Watch/dp/B000A8BUBU

> Maker and model number if possible.

Back of the watch says Lance 4 680087

WA0020 WG88-0010 0485776 MADE IN CHINA

That's all I can find. The operation instructions are on a 19" x 25"
single sheet, double sided, heavy in pictographs and multiple languages,
but I see no technical details.

> If you still have the
> documentation or box, they should the FCC ID number. I might need
> that to determine the type of sensors it uses. Don't be surprised if
> the altimeter/compass module and case are made by two different
> companies, and sold by a third company.
>
> MEMS sensors can be very fragile. I've read about MEMS sensors in
> watches that were killed by sudden changes in air pressure.
>
>> But its altimeter long ago lost its
>> mind. When powered up, it claims continuous and rapid altitude gain.
>> Nike wanted a fortune to "fix" (probably replace) it many years ago.
>
> I've seen that on rarely recent MEMS sensors that use resistive
> bridges.
> <https://www.allaboutcircuits.com/news/rohms-waterproof-barometric-pressure-sensor-is-more-than-a-weather-forecaster/>
> When one of the four bridge resistors goes open circuit, the bridge
> becomes drastically unbalanced and shows a ridiculously high or low
> altitude. That's only one type of sensor. If it were piezo-resistive
> or piezo-electric, things fail differently. Incidentally, negative
> altitudes are possible with this type of failure. I have some of the
> necessary SMD tools necessary to do the repair, but lack a supplier
> for a currently unspecified MEMS sensor.
>
>> I suppose I could fire it up, go for a bike ride and do some bragging
>> here about my climbing prowess...
>
> You're making it difficult for me to be inspired.

Please don't let this take time away from educating Tom. ;-)

I've got a couple of nice old wall-mounted mechanical barometers around
here. Those I can understand!

I could strip the mechanism out of one, calibrate it for altitude and
affix it to the handlebars of one or another bike.

Steampunk!

--
- Frank Krygowski

On Thursday, June 30, 2022 at 4:28:42 PM UTC-7, Roger Merriman wrote:
> Tom Kunich <cycl...@gmail.com> wrote:
> > On Thursday, June 30, 2022 at 2:10:28 PM UTC-7, Lou Holtman wrote:
> >> On Thursday, June 30, 2022 at 10:19:39 PM UTC+2, deaco...@gmail.com wrote:
> >>> I have posted this discussion before but it still bugs me. Today I ride
> >>> 64 miles on some rolling hills but nothing considered climbing. My
> >>> Garmin 935 has elevation gain 1263. RIde withe the GPS says I did 1639
> >>> feet of climbing. I would think that is based on terrain that they have
> >>> in maps and data and pretty accurate. My 935 does has barometric
> >>> altimeter but would that be more accurate? No matter what ride I do
> >>> there is always a difference with a error rate around 25%. That seems alot to me.
> >>> Deacon Mark
> >> How was the weather? Stable? If Yes, trust your Garmin.
> >
> > I'm not real sure of that. My grade seems to move very slowly and i would
> > expect a fairly large error. But since I haven't been doing any climbs
> > for the last 6 weeks I really have nothing to base that on. Perhaps it
> > has a large delay in the gradient but the altitude reads accurately. On
> > one of my climbing rides, there is a spot that is 900 feet and another
> > that is 1100 feet so that I can compare. The 1100 is followed by a
> > descent followed by another steep climb that I have never successfully
> > measured since getting to the top of that always has be burned out.
> >
> My Garmin 830 + Garmin connect/Strava give exactly same figures it should
> be fairly close.

I haven't gotten my 830 back yet but one of the reasons that I sent it back was because it was showing a 12% error in GPS distances one day to the next.

I am pretty certain that the rate of climb lags behind the actual rate of climb but that the actual altitude reads correctly.

Tom Kunich <cyclintom@gmail.com> wrote:
> On Thursday, June 30, 2022 at 4:28:42 PM UTC-7, Roger Merriman wrote:
>> Tom Kunich <cycl...@gmail.com> wrote:
>>> On Thursday, June 30, 2022 at 2:10:28 PM UTC-7, Lou Holtman wrote:
>>>> On Thursday, June 30, 2022 at 10:19:39 PM UTC+2, deaco...@gmail.com wrote:
>>>>> I have posted this discussion before but it still bugs me. Today I ride
>>>>> 64 miles on some rolling hills but nothing considered climbing. My
>>>>> Garmin 935 has elevation gain 1263. RIde withe the GPS says I did 1639
>>>>> feet of climbing. I would think that is based on terrain that they have
>>>>> in maps and data and pretty accurate. My 935 does has barometric
>>>>> altimeter but would that be more accurate? No matter what ride I do
>>>>> there is always a difference with a error rate around 25%. That seems alot to me.
>>>>> Deacon Mark
>>>> How was the weather? Stable? If Yes, trust your Garmin.
>>>
>>> I'm not real sure of that. My grade seems to move very slowly and i would
>>> expect a fairly large error. But since I haven't been doing any climbs
>>> for the last 6 weeks I really have nothing to base that on. Perhaps it
>>> has a large delay in the gradient but the altitude reads accurately. On
>>> one of my climbing rides, there is a spot that is 900 feet and another
>>> that is 1100 feet so that I can compare. The 1100 is followed by a
>>> descent followed by another steep climb that I have never successfully
>>> measured since getting to the top of that always has be burned out.
>>>
>> My Garmin 830 + Garmin connect/Strava give exactly same figures it should
>> be fairly close.
>
> I haven't gotten my 830 back yet but one of the reasons that I sent it
> back was because it was showing a 12% error in GPS distances one day to the next.
>
> I am pretty certain that the rate of climb lags behind the actual rate of
> climb but that the actual altitude reads correctly.
>

The recorded curve both on the Garmin and on Connect/Strava seem correct
I’ve not gone into them in detail.

I’ve only to date ever noted that it might be wrong, and that was the
displayed altitude as the pressure dropped and moved past the figures where
wrong below sea level I think!

I’d assume that it was corrected once uploaded or even on the device but I
haven’t checked.

Though I do tend to look at figures but a low flat area I’d probably not
look at elevation anyway!

Roger Merriman