Re: correct air pressure

[Chris Alston <alstonc@odrge.odr.georgetown.edu>]

>X-Sender: billmcc@hargray.com
>Date:         Thu, 26 Mar 1998 12:46:21 -0500
>Reply-To: Medical Physics Mailing List <MEDPHYS@LISTS.WAYNE.EDU>
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>From: Bill McCarthy <billmcc@HARGRAY.COM>
>Subject:      Re: correct air pressure
>To: Multiple recipients of list MEDPHYS <MEDPHYS@LISTS.WAYNE.EDU>
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>George,
>I don't think there is a good way to intercompare barometric pressure
unless you are standing next to the standard barometer.  Any high quality
mercury barometer is a "standard" barometer because it measures BP on an
absolute basis (mm of Hg supported by the atmosphere).  Don't forget the
temperature correction and to insure the murcury is clean.
>
>I go to the local Air Forces Field which has some sophisticated barometers
that are recalibrated every week because people's lives depend on it. I
carry my aneroid barometer with me and use it as a transfer standard to
calibrate the others when I'm standing next to them.
>
>Obviously there is a strong correlastion between height and BP and it's
hard to tell exactly how high you are at any point on earth or how high the
guy on the other end of the phone is (not a pun).
>>
>>You wrote:
>>Dear Medical Physics subscribers,
>>
>>Any comments and/or references on how to correct for altitude and latitute on
>>a barometer calibrated at the sea level would be appreciated. I am interested
>>(for beam calibration) in corrections required by both a mercury and non-
>>mercury barometer. I made an audit at a radiation therapy department and there
>>was a discrepancy of 20 Hg mm between the readings of the barometer and the
>>air pressure given by the weather service. The "local" physicist says that it
>>is because he made the "corrections" while the weather service gives the sea
>>level pressure; the weather man says that this is the pressure measured in
>>their yard (close to the hospital; so I take it as being the "real" or
>>absolute pressure, the one which I need for Cpt). How do I solve the problem?
>>
>>Thank you in advance for your comments.
>>
>>George Capatina, Ph.D.
>>physics92@aol.com
>>
>