I like simple mechanical old style pencil gauges. Reliable, and so cheap you can have two or three and compare. I went into a shop once that had a bucket of them and 2 or 3 $ each, and asked if I could test a few. He said yes, so I grabbed a hand full before he could change his mind, went out and started testing. Consistency was good, not perfect but certainly good. I picked one that was right in with the bulk of them. Note that ALL were within two psi.
And yes I adjusted for the slightly lower pressure as testing continued. 
Still have it 20 years later, still good. And I have several digital gauges, and all require batteries of course and all are usually dead when I want to double check.
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Grant Johnson
Seek, and ye shall find.
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Inspiring, Informing and Connecting travellers since 1997!
www.HorizonsUnlimited.com
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