You need to find a known accurate gauge. Auto repair shop may accomodate you.
When I want to check a pressure gauge, I compare it to several I have in my tool chest. These all measure very close to the same value, so I assume that they are statistically accurate enough to identify a bad gauge.
Let me know if you want to drive down to San Jose, and we can examine your gauge. Or, buy a general-purpose pressure gauge from Harbor Freight, and compare.
Ed in San Jose '97 540i 6 speed aspensilber over aubergine leather. Build date 3/97. Golden Gate Chapter BMW CCA Nr 62319.
Last edited by edjack; 02-11-2011 at 12:52 PM.