Resolution, precision, accuracy, repeatability

✎ This article/section is a stub — some half-sorted notes, not necessarily checked, not necessarily correct. Feel free to ignore, or tell me about it.

Accuracy is how far measurements are from their true value (which is sometimes a standard value).

how you know that true value itself to more accuracy is a good question, though mostly amounts to more work.

Precision is largely about how consistent measurements are

measurements can be very precise but not at all accurate - e.g. a precision instrument that is consistently off to one side due to bad calibration

it may then be that calibration is the only thing keeping it from being a lot more accurate -- OR things may be a lot messier and more complex

Resolution is (usually) the units in which is reported (or controlled)

resolution often hints at the order of accuracy and/or precision, but this can be misleading

yet high resolution is also a great way to hint at more accuracy and/or precision than you really have

e.g. does your 4-digit multimeter always show accurate digits? How would you tell?

Repeatability asks that when you later return to the same true value, how stable your measurement of it is

this is much like precision, but focuses more on the tool or the machine, than the measurement.

If repeatability is contrasted with reproducibility, then

repeatibility is often a "can one person on one instrument get the same measurement again", and

reproducibility is often a "if you have different operators, and/or different instruments, do they get the same measurement?"

Resolution and repeatability are also words used when asking how well you can actuate/control something - which also makes things more complex because both the control and the measurement of the result may each have their own precision/accuracy details.

If my multimeter shows me 1.153 volts, it makes it easy to assume its accuracy is three digit's worth (around 0.1%).

But generally, multimeters shouldn't be assumed to be better than 1%, both because more extreme values (e.g. many-megaohm) are often harder to measure, and because cheap ones don't care as much about calibration. Cheap + extreme value combination may be more like 5%. And those figures are not very easy to find.

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