DEFINITION OF TERMS

The closeness of agreement between a measured quantity value and a true quantity value of a measurement.

The documented comparison of a measurement device (to be calibrated) against a traceable reference device. It is generally achieved through a two steps process firstly involving comparing measurements from a system under test with a set of reference values and then secondly using the result of the comparisons in step 1 to correct the results of subsequent measurements.

For a measurement to have value, all measurement systems must be consistent with each other, giving rise to the term “consistency”. See also repeatability.

A condition that is always present in measurement and therefore does not mean there is a problem with your measurement systems, procedures or routines. All measurements are subject to several errors, and there are many types of error of which random and systemic are the most common. (See also Margin of error).

We know that errors are fundamental. What we need to determine in the field of measurement is margin of error. This calculation quantifies how wrong a measurement might be. While errors themselves are a constant and not inherently problematic, it is extremely important to determine the margin of error.

The value of the metric measured in any way and expressed (in meters, or kilograms, etc.) after measuring is complete. The measured value number tells you that a measurement has been taken, and how it has been taken.

Precision is the closeness of agreement between measurement outcomes obtained under stipulated conditions. It reflects the distribution of random errors and differs from accuracy in that it does not relate to the true value of the object being measured.

A reference unit is anything that can be measured or quantified in some way. It may be an object, or it may be something else, for instance time.

Refers to set of conditions (known as “repeatability conditions”) wherein results are obtained using the same measurement method on identical test items in identical (or near identical) conditions. Repeatability is an attempt to avoid sources of error in making a measurement, so the results can be said to be repeatable.

Refers to how big a deviation from an expected value is acceptable in a given situation. If a measurement or manufacturing process has a tight tolerance, the allowable range of variation will be narrow. In contrast, a looser tolerance will allow for a wider range of acceptable values.

The provision of a reference to a recognized benchmark, for example a European Standard class rating, which confirms the accuracy of a measurement. A measurement system that has such a (third party) reference is said to be traceable.

The actual physical weight/length/width or other measurable parameter of a specific object. An object’s true value is absolute, and it can never be exactly determined. When we measure, we want our measured value to align as closely as possible with its expected true value.