In a RSES tech tip I read Quoted directly from Ritchie Engineering about analog gauges "Why Zero Out A Manifold Gauge?"
It said a gauge can get off 0 due to change in altitude or barometric pressure. It is important that you set it back to 0 before charging.
FWIW A bourdon tube analog gauge is not affected by by altitude or barometric pressure. If your open to ATM gauge is reading 0 at sea level and you take it up to 10,000 ft open to ATM it will still read 0. Additionally if you are using the PT chart printed on the gauge face for charging or troubleshooting at altitude with the gauge open to ATM you should adjust the needle off 0 and set it to the equivalent psia of the environment you are in.
There's some threads around here that suggest calibrating the gauges in the middle of their operating range. Get a bottle of refrigerant that's at a stead temp, hook your gauges up to it, find the temp of the freezone, and adjust it so it reads correctly there. Ignore what it's on when there's no pressure.
Makes sense to me, I'd rather have it accurate in mid swing (much closer to where I generally need the measurement taken) than 0.
I've done it to my gauges a couple times, but I'll admit, I don't touch my gauges much at all. It is admittedly easier to just set them at 0 when they get way off...
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yes you have to calibrate an analogue gauge at the top center of its' chart (the most accurate part)......none of my analogues read zero after being calibrated.
Not really....I expect it. It's only a problem doing refrigeration work....haven't done any of that for a few months, so no biggie right now......if i get into it again, yes, it is a bummer!!LOL!!
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Originally Posted by mark beiser
