Definition
Measurement is the act of determining a specific physical quantity, such as a length, diameter, or angle, using a calibrated instrument, from a simple caliper to a coordinate measuring machine (CMM). It is the basic building block inspection is built from: an inspection plan specifies what to measure, and measurement is how each individual value is actually obtained.
Why measurement uncertainty matters, not just the raw reading
A measurement is only as trustworthy as the calibration and appropriateness of the instrument and method used, which is why measurement uncertainty, not just the raw reading, matters for verifying a tight tolerance.
Where measurement requirements come from
Implied by each dimension and tolerance on a drawing, each of which requires an appropriate measurement method and instrument to verify.
Common mistakes
Assuming any instrument capable of producing a number is adequate for a given tolerance; an instrument's own measurement uncertainty needs to be well within the tolerance being verified, not just capable of producing a reading.
A measurement is only as trustworthy as the calibration and appropriateness of the instrument and method used, which is why measurement uncertainty, not just the raw reading, matters for verifying a tight tolerance.
See how Blake reviews a partFrequently asked questions
Is measurement the same as inspection?
Measurement is the individual act of determining a value; inspection is the broader activity of checking a part's requirements, often using multiple measurements.
Why does instrument calibration matter for measurement?
Because an uncalibrated instrument can give a confidently wrong reading, undermining the trustworthiness of the measurement.
Can any instrument measure any tolerance?
No, an instrument's own measurement uncertainty needs to be appropriately small relative to the tolerance being verified.