Is your caliper really that accurate and calibrated? In my experience you need a calibrated micrometer for that level of accuracy, especially to get a consistent measurements between several persons

Yes, reputable digital calipers are fine for thousandths of an inch. A micrometer is good for further precision and when you what more consistent measurements of softer materials. For example, if I measure my set of - gage pins, the caliper agrees exactly with the spec (a .210 pin reads 0.2095), and it's pretty hard to torque down too tightly on hardened steel. But if they were nylon and not steel, you'd probably get better repeatability with a micrometer. (And it's worth noting that the pins generally aren't actually half a thou smaller, a micrometer reads 0.20990. If 4 ten-thousandths of an inch are important to your project, yeah, you need a micrometer.)

ah, thousands of an inch, I'm not American and was thinking thousands of a mm

Yup. These calipers that measure to .0005 of an inch only show hundredths of a mm (10 microns).

As for language, "thou", short for thousandths of an inch, is kind of the base unit in imperial machining. That's why the next one down is "tenth" in the vernacular. It's very confusing because 100 thou is one tenth of an inch, but you'd never call it a "tenth" even if "inch" is implicitly the base unit. Also confusing is that there are SI prefixes for all of these things, but they aren't in use. (Why not "milliinch"?)

Finally, one more advantage of the metric system; to measure 1 micrometer, you need a tool called a micrometer. That's easy to remember!

Yes it is. It and my mics are calibrated to at least the thousandth. The shop has a 6" mic set on the ten-thousandth. But nobody uses that one because that's a level of detail that is just amazingly frustrating to chase.

>between several persons

This is just wrong. Rule one of precision equipment - do not touch my precision equipment.

Hum... Since I've brought a digital caliper that allowed reading sizes with actual 0.01mm precision instead of "guessing it's around X", I've noticed I have no object around that won't compress by something larger than that amount when I apply reasonable amounts of force into the caliper.

I'm also sure it's not calibrated to this level, but that doesn't hurt relative measurements.

That’s why calipers ought to have those tiny “rolls” that you can turn to move them, instead of pushing, this way you can’t “overtension”.

My analog ones do have a push wheel that slips easily.

The nice thing about analog is they don’t confuse you about precision - a digital caliper could be only precise down to .01 and yet show .0001 increments.

For many things like a bathroom scale precision isn’t really needed anyway.