On 30/06/2020 23:13, Dennis Lee Bieber wrote:
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> {Strange -- Topo map shows my house at 650ft, calibrating my GPS altimeter
> for 650ft gives barometer 29.94 -- but setting my analog altimeters for
> 29.94 is showing altitude of 725ft. I suspect it is lack of temperature
> compensation -- the analog altimeters were consumer grade: Thommen Altitrek
> and Sun Altimeter 203... A few years ago I looked for the pro-grade
> Thommen, but all Thommen units had been discontinued. The pro-grade version
> included thermal compensation}

OP: Don't forget to check the datasheet for the accuracy:

https://cdn-shop.adafruit.com/datasheets/BST-BMP180-DS000-09.pdf

Dennis: There are two altitudes which can be quoted:

   MSL: above mean sea level

   HAE: height above reference ellipsoid

In Edinburgh there's a 50m difference according to CGPS on two systems
here, and that seems too high to me.

   https://www.esri.com/news/arcuser/0703/geoid1of3.html

--
Cheers,
David
Web: http://www.satsignal.eu

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