1. conformity of an indicated value to an accepted standard value, or true value. Quan­titatively, it should be expressed as an error or an uncertainty. The property is the joint effect of method, observer, apparatus, and environ­ment. Accuracy is impaired by mistakes, by systematic bias such as abnormal ambient temperature, or by random errors (impreci­sion).

2. degree of freedom from error, that is, the degree of confor­mity to truth or to a rule. Accuracy is contrasted with precision, e.g., four‑place numbers are less precise than six‑­place num­bers; nevertheless a properly computed four‑place number might be more accurate than an improperly computed six‑place number. 3. ability of an instrument to indicate the true value of a measured physical quantity. Compare precision, reliability, repeatability.

ACH (ACPH)