I have never noticed anything in the SI Brochure or NIST SP330 requiring pressure to be stated on an absolute basis vs gauge. Obviously the other side is atmospheric pressure. Since proper procedure is to purge the a/c system to a vacuum and refill with refrigerant, absolute pressure might be a better choice here. But in most geographic areas the flucuation in local pressure (with weather, or even elevation above sea level) would be minor vs the accuracy of the gauge. However, I think it is always the same gauge and they paint different numbers on the dial face.
--- On Thu, 7/9/09, Michael Payne <[email protected]> wrote: From: Michael Payne <[email protected]> Subject: [USMA:45330] Vacuum display To: "U.S. Metric Association" <[email protected]> Date: Thursday, July 9, 2009, 3:53 PM I was under the impression SI pressure in Pascal's was always positive. Earth pressure near 100 kPa, Mars pressure near 20 kPa, outer space near 0 Pa. Is this correct. I see the gauge from Yellow Jacket has an area listing a minus side. Mike Payne
