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.

Precision is largely about how consistent measurements are - the trial-to-trial variability

measurements can be very precise but not at all accurate

e.g. a precision instrument that is simply not calibrated may be consistently within a very narrow margin - but not accurate to the true value (because all those measurements are off the true value)

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

Accuracy is how far measurements are from their true value

how you know that true value itself to more accuracy is a very good question, with only longer answers

assuming you have precise measurement, the accuracy is often off the true value by a relatively fixed offset

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

resolution often hints at the order of accuracy and/or precision

but you see a lot of cases where assuming 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 know?

Repeatability, also known as 'test-retest variability, asks that when you later measure the same thing, 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

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

Semi-relatedly, resolution and repeatability are also words used when asking how well you can actuate/control something

which muddies the water because both the control and the measurement of the result have their own precision/accuracy details