## Metrology

*The science of measurement, embracing both experimental and theoretical determinations at any level of uncertainty in any field of science and technology.*

## Accuracy vs. Precision

Accuracy attempts a measurement as close as possible to a known value and is the degree to which a given quantity is correct and free from error.

Precision attempts multiple measurements to be as close to each other as possible and is the number of digits used to perform a given measurement.

*"Precision is measured with respect to detail and accuracy is measured with respect to reality."*

But:

*"Accuracy is limited by the precision with which physical markings can be drawn, reproduced, viewed, and aligned."*

And; precision is independent of accuracy:

*"For example, if on average, your measurements for a given substance are close to the known value, but the measurements are far from each other, then you have accuracy without precision." ^{[1]}*

While the accuracy of a number is given by the number of significant digits to the right of the decimal point, the precision is the total number of significant digits.^{[2]}

### Significant Digits

The number of significant digits (or significant figures) is the number of digits needed to express the number to within the uncertainty of calculation. For example, if a quantity is known to be 1.234 ± 0.002, four figures would be significant.^{[3]}

### Measuring Devices

- Accuracy is determined and limited by the precision with which physical markings can be created and reproduced, as well as read and aligned to the corresponding object to be measured.
- The maximum achievable precision is ± half of the smallest division of the scales.

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