Resolution, precision, accuracy, repeatability: Difference between revisions
Jump to navigation
Jump to search
mNo edit summary |
mNo edit summary |
||
| Line 5: | Line 5: | ||
: how you know that true value ''itself'' to more accuracy is a good question, though mostly amounts to more work. | : how you know that true value ''itself'' to more accuracy is a good question, though mostly amounts to more work. | ||
| Line 37: | Line 25: | ||
: If repeatability is contrasted with '''reproducibility''', then | : If repeatability is contrasted with '''reproducibility''', then | ||
:: repeatibility is often a "can one person on one instrument get the same measurement again", and | :: 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 | :: 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. | |||
<!-- | |||
Accuracy is sometimes split into relative accuracy and absolute accuracy. Not all definitions are the same here, but usually, | |||
: relative accuracy is about whether comparisons are accurate to a given reference | |||
: absolute accuracy where that reference is reality. | |||
For example, consider having a map of houses, and a map of roads. | |||
: Both can have high relative accuracy, in that the distances between objects are the distances in reality. | |||
: But they may not be georeferenced with the same assumptions, meaning they may be a few meters off of reality -- and thereby also probably a few meters offset from each other | |||
:: (and not necessarily off by a constant. You may need to creatively rubber-sheet things to get them to match well ''enough'') | |||
In other contexts, the same ideas lead to different details of importance, and different summaries. | |||
For example, measurement instruments | |||
Relative accuracy: Inherent instrument accuracy relative to calibration standards. It includes stability, temperature coefficient, linearity, repeatability, and calibration interpolation error. | |||
Absolute accuracy: The sum of the relative accuracy and the uncertainty of calibration standards. | |||
--> | |||
Revision as of 14:48, 9 August 2023
✎ 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.
-->