Re: Garmin altitude problems

On Thu, 08 Aug 2024 10:18:39 GMT, Roger Merriman <roger@sarlet.com>
wrote:

Jeff Liebermann <jeffl@cruzio.com> wrote:

On Wed, 07 Aug 2024 17:57:59 GMT, Tom Kunich <cyclintom@yahoo.com>
wrote:
 

The formula for change in altitude with air pressure in the lower
atmosphere (about to 35,000 feet) is:

 
Nope.  From what's left of your formula, I'll assume you're trying to
calculate the air pressure at a given altitude.  There is no *change*
in altitude involved.  Looks like you lost all the Greek letter
symbols and formula symbols. 
 

P=Pb[1
Where:
 
 
Pb
TM,b
LM,b
h
hb
R
g0
M

 
That unreadable mess should look something like these:
 
"Atmospheric Pressure Calculator"
<https://calculator.academy/atmospheric-pressure-calculator/>
 
"Air Pressure at Altitude Calculator"
<https://www.omnicalculator.com/physics/air-pressure-at-altitude>
 
Note that you need to know the barometric base pressure (Pb) at sea
level for such a calculation to work.  It's NOT going to work if your
riding up or down a hill where the barometric pressure might change.

 

In fairness the 830 recalculates on start up every so often particularly if
it’s a changed location or it may well do so every time but don’t watch it
start up in general.
>
Roger Merriman

Garmin works in mysterious ways.  Garmin's self calibration algorithm
is a bit stranger than one might expect.  For example:
<https://forums.garmin.com/sports-fitness/cycling/f/edge-830/174850/elevation-auto-calibration>
"Every time I start to record an activity on my Edge 830 I get this
message "Elevation calibrated to location" and immediately the
elevation number goes up by +/-12m out of the blue with me standing
still in the same spot.
The problem is that the elevation shown right before I press the
record button (before the "auto-calibration) is more accurate than the
one modified."
"The value is coming from the saved location that is near your
starting point."

I seem to recall reading somewhere that Garmin recommends calibration
before starting on a ride.  I'm too lazy to find where Garmin said
that.

However, that message is over 5 years old and the problem might have
been fixed long ago with a firmware update.

The barometric altimeter accuracy in the Garmin Edge 830 is specified
at +/-50 ft accuracy (which is better than the +/-400 ft accuracy for
the GPS).  There's also a +/-10 ft error for reasons unknown:
<https://support.garmin.com/en-US/?faq=sFMkjQFdnZ99DcunfAue66>
"Elevation accuracy of +/-10 meters is for any given reading during an
activity, not the total elevation gain/loss at the end of an
activity."

Very mysterious methinks.


--
Jeff Liebermann                 jeffl@cruzio.com
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