On Fri, 02 Sep 2016 09:05:14 -0700, Jeff Liebermann
wrote:

On Fri, 02 Sep 2016 12:48:18 +0700, John B.
wrote:

But how do you know that the calibration gauge is reading correctly?
Or your digital gauge, for that matter. A proper testing station will
include a dead weight tester to calibrate the calibration gauge(s) :-)

Use The Force(tm) Luke!

It's actually quite easy. I drag myself over to the local
multiversity, prostate myself before the keeper of the calibration
lab, beg forgiveness for previous equipment damage, issue the required
bribe, and calibrate the indicated reading of my gauge against one of
their dead weight pressure tester:
https://www.google.com/search?q=pressure+calibrator&tbm=isch
I discovered that some of my cheap gauges exhibit some hysteresis
making calibration more difficult:
https://www.dwyer-inst.com/articles/industry/powderbulk/understanding-pressure-sensor-accuracy/understanding-pressure-sensor-accuracy.cfm
My piezo digital gauge doesn't have the problem.

Once I have a calibrated gauge, the rest of my gauges and pumps are
calibrate against it, usually just at key reference points, which
coincide with my favorite pressure settings for my various tires.

Hint: Don't use an automotive oil pressure gauge or sensor. They do
work and are very rugged, but they have horrible accuracy and
linearity problems. They also respond very slowly to changes in
pressure.

I wonder if the LBS could use this as a draw for the local cyclists.
Free bicycle pump gauge calibration. Bring in the pump, we supply the
equipment, and you do all the work. I suspect a fair number of pump
gauges have problems.
https://www.google.com/search?q=bicycle+pump+pressure+calibration

:-)
My experience is that most of the small cheap gauges do have errors,
but I would also guess that the average cyclists doesn't actually
care. My guess is that the average guy pumps the tires up to a number
between the big number and the little number embossed on the tire wall
and rides away contented.

At least, even here, there was sufficient discussion when the subject
came up to show, I believe that even the elite riders really aren't
really that knowledgeable about the effects of tire pressure.

But having said that, snake bite flats aside, what is the actual
importance of tire pressure? What will be the actual (not calculated)
difference in time for a, say 10 mile TT, with 10 psi more or less
pressure in the tires?
--
cheers,

John B.