There is no universal number of readings. Choose a documented sampling plan based on the variation you need to represent—and be clear about whether you are repeating one position, repositioning, sampling locations or sampling a lot.
Four different kinds of readings
Repeated readings
Test short-term instrument variation at one stable presentation.
Repositioned readings
Include operator placement and local surface effects.
Multiple locations
Estimate within-part spatial variation.
Multiple parts
Estimate variation across a lot or batch.
Start with a pilot plan
Measure defined positions on representative good parts, record individual values and compare repeatability with spatial variation. Then set a reading count and location pattern that represent the product. Specify whether software averages spectra, coordinates or difference values; these are not generally interchangeable.
An average can hide a defect
Relative to Lab (50,0,0), samples at (49,0,0) and (51,0,0) each have ΔE76 = 1, while their mean Lab is (50,0,0), ΔE76 = 0. This is a calculation example, not experimental data. Use individual-position limits when local uniformity matters.
Averaging improves an estimate of a representative mean; it does not remove instrument bias or physical non-uniformity. Link your plan to repeatability, sample preparation and tolerance setting.
Last reviewed 20/09/2026 · Level: Fundamental
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