[instarx]

I'd also like to add a pet peve of mine: the apparent (and totally bogus) precision people assign to digital gauges of all types. In the picture of the pressure gauge above you might think the tire pressure was 28.5 psi. In fact the gauge only has half a digit of precision, meaning the pressure is anywhere between 28.25 and 28.75 psi. (I have one of these and the gauge only reads 27.5, 28.0, 28.5...etc.).

This raises and interesting possibility: two tires measured at 28 psi with this gauge may be much further apart in actual pressure than two tires measured with this same gauge at 28 and 28.5 (which would happen if the actual pressures were 28.2 and 28.3 psi).

Having said that, it is only an academic problem. In my opinion it doesn't matter if tire pressures vary by half a psi. Precision for precision's sake is wasted effort.

For example, for the past 20 years there has been a strict standard for the velocity of the air jets that blow dust from the clothing of people entering Class III and IV clean rooms. I don't remember the exact value any more, but it is something like 85 feet per second. Millions of dollars have been spent making sure that the air-wash in clean rooms around the world have this velocity. Entire systems have been torn out and replaced to achieve this velocity. Clean rooms have been de-certified because they only had 80 fps wash air. What most people do not know is that the two researchers who established this "best" value arrived at it by holding a rag out a car window and noting the speed where it flapped the most.