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Study Notes: Calibration

Calibration is a process that allows the operator to determine if a piece of testing equipment is performing to the degree of accuracy and precision required. Calibration will vary depending on the equipment being used. For instance, calibration of an optical microscope is very different to that of an analytical balance or a pH meter.

Accuracy relates to the ability of the machine/operator to measure as close as possible to the 'true value' of the measurement (in reality the true value is never achieved as there are variations in all measuring systems).

Precision relates to the ability of the machine/operator to give the same reading when the same thing is measured a number of times. In this instance, weighing the same object ten times in succession should give ten readings that are very close together. (We would not necessarily expect them to be identical, due to variations in the measuring system and conditions).

Note: a piece of equipment can be precise yet be inaccurate.
For example, suppose that the true value for the mass of a standard is 10.1200 g and five consecutive readings of this standard give the following results:

3.3456 3.3467 3.3412 3.3443 3.3457

The balance is precise (as the five measurements are close to each other) BUT the balance is certainly NOT accurate (as the true value is 10.1200 g)!

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