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Author
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Topic: Recent tech support on baro calibrations
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David Burch
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posted November 16, 2023 04:13 PM
... which might be of interest to others.
On Nov 16, 2023, at 2:07 PM
[email protected]
I am studying your book „Modern Marine Weather“ very carefully and try to calibrate my on-bord barograph using starpath app and NDBC data. Following your calibration procedure on page 248 I do not understand the correction of the example: 1005.2 +((48/60)*(2.9/3) = 1005.2 + 0.8 (OK) = 1012 (not OK).
Do I miss some something or is this only a test for the diligent reader (😉)?
Bernd / SY Alita
Von meinem iPad gesendet
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Hi Bernd,
You are clearly a diligent reader and indeed the type of navigator we admire… namely you do not let prominent observations go by unexplained.
In this example it appears you are calibrating using an official pressure report that is updated hourly and includes the official pressure trend which is the change that took place in the past 3 hours, which is what we have to assume the rate of change will be in the future if we do not learn more.
in this case, the latest report was at 1700 and at that time the pressure was 1005.2 mb with a rate of change of 2.9 mb per 3hr, which is a rate of change of (2.9/3)mb/hr. The calibration time is 1748, so this is (48/60)hr past 1700. From the tendency then we would expect this pressure to have risen at 1748 to value at 1700 + (48/60) x (2.9/3), which is a correctioin of +0.8 mb
In other words, we are not just going to a primary source and reading the pressure, we are correcting it for the change between now and when it was recorded.
Hope that helps.
— david
David Burch, PhD, FRIN
Starpath School of Navigation
Seattle, WA
From: Starpath, Seattle, WA
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