The concept of negative pressure is purely arbitrary and is relative to a reference point (atmospheric pressure). The absolute pressure in a vacuum is zero (of whatever units).
Bill Potts, CMS Roseville, CA http://metric1.org [SI Navigator] >-----Original Message----- >From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] >Behalf Of Pierre Abbat >Sent: Saturday, February 12, 2005 03:58 >To: U.S. Metric Association >Subject: [USMA:32244] Re: pseudometric units > > >On Friday 11 February 2005 22:29, J. Ward wrote: >> The climate scientists I work with measure atmospheric pressure in >> hectopascals, e.g., 1014 hPa. And the stickers inside the door of both >> my cars specify tire pressure in kPa [psi]. >> >> On the other hand, nearly all vacuum equipment I have worked with reads >> pressure in torr, millitorr, and (occasionally) "microns," as in >> micrometers or mercury. I have not seen pascals used for vacuum systems. > >I have seen a pressure gauge that had two different units, one for >positive >pressures and one for negative ones! (I don't remember what they were.) > >phma >-- >le xruki le ginxre xrixruba xu xrula cu xrani? >
