correct air pressure -Reply

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

>Date:         Thu, 26 Mar 1998 08:48:26 -0600
>Reply-To: Medical Physics Mailing List <MEDPHYS@LISTS.WAYNE.EDU>
>Sender: Medical Physics Listserver <medphys@lists.wayne.edu>
>From: "Frank R. Borger_(FRB)" <FBORGER@GAMMEX.COM>
>Subject:      correct air pressure -Reply
>To: Multiple recipients of list MEDPHYS <MEDPHYS@LISTS.WAYNE.EDU>
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>>>>>>>>>>>>>>>>
>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
>
><<<<<<<<<<<<<<<
>
>At my previous place, we used a rule of thumb of 0.3mm difference between the
>first floor, (where the linacs were,) and the 2nd floor, (where the mercury
barometer
>was in the physics office.) You could really see this with a digital
electronic barometer.
>
>Ballpark, a 20 mm difference is equivalent to somthing like 300feet
elevation change.
>
>An airport can usually give you uncorrected barometer readings, (for
altimeter settings,)
>but you still have to fudge for difference in altitude between you and the
airport.
>
>Frank R. Borger, Senior Support Engineer
>Gammex-RMI, Middleton WI
>608-828-7289 fborger@gammex.com
>
>The opinions expressed here are strictly mine,
>and do not reflect the views of Gammex-RMI.
>