@elo.egypte
In that case you cannot fix the issue.
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I just came across this old thread …
I don’t know if the #ALT# tag is wrong or not, but you can calculate the altitude yourself from the #ATM# tag.
refer:
where P is replaced by #ATM# ( which is in hPa )
and P0 by 1013.25 hPa
Note that the formula assumes that the pressure at sea level is 1013.25 hPa, but this is only sometimes true as high and low pressure weather systems roll through. The error due to weather can be very large, around 100m per 12 hPa of pressure change. Low pressure systems will result in higher than true altitude and the opposite for high pressure systems.
Still it can be fun to play with and can also still be used to estimate the change in altitude as you climb a hill for instance. Take note of the altitude on your watch when you start and subtract that from the value at the top of the hill and the difference will be pretty close to the height of the climb.
If you have access to VARs then you can also amend the expression above to correct the #ATM# value by the offset from standard pressure due to weather.
ie. replace P with (#ATM#+#VAR_1#)
where #VAR_1# represents the change in pressure due to weather
ie. set #VAR_1# to round (1013.25-{actual sea level pressure from a near weather station })
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I have been looking into this.
Seems to me, the #ALT# is quite accurate in terms of meters. In my location, anyway…
But if I switch to Imperial (in Facer App) on my watch, it is way off.
It looks to me that Facer converts meters to feet by 2x 3.28, instead of only once.
So with the following formula, the value in feet is correct (dividing the feet value by 3.28):
$#UNITSYS#=IMPERIAL?(round(#ALT#/3.28)) ft:(round(#ALT#)) m$
But of course, if Facer fixes the issue, then the formula is no good…
So coming back to calculating the altitude using #ATM#.
Since we do not have the “ln” function, we need to use what we have: log, log2 or log10, exp, expm1.
So I figured out (with the help of AI) that the following formula can be used:
Altitude = TK/L * expm1(0.13188 * log2(P0/P))
L (Lapse constant) = 0.0065 K/m
the rest as above.
So putting that into a formula (metric):
(round(((#WCT#+273.15)/0.0065)*(expm1((0.13188)*(log2(1013.25/#ATM#))))))
My test on my watch:
hPa = 944
Temp = 20C
ALT = 597m
with ATM formula, I get: 615m
and in feet, using : ALT/3.28 = 1958 ft
looks pretty good to me!
Imperial:
If you want the ATM formula for Imperial setting, then you will have to replace
#WCT# + 273.15
with:
TK = (#WCT# − 32) × 5/9 + 273.15
which can be simplified as (#WCT# + 459.67) × 5/9
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Sadly though, even after all your work on this, #ALT# and #ATM# are both not supported in WFF in Facer.
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@kd7eir I’m curious about you username. It looks like an amatuer radio call sign, but it doesn’t come up in any call sign databases.
You are using the wrong data base. He is an amateur radio operator, but he has a different callsign now. I’m also a licensed ham and a GMRS operator, but I don’t use my callsigns on Facer.
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Yes, I was once young and naive.
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I was using qrz.com which uses the FCC database. Maybe it doesn’t have old callsigns linked anymore.
73s, KE3JU
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