Calibration · Glossary

What is Repeatability?

standard deviation or max spreadCalibration

Repeatability is the closeness of successive readings of the same input under the same conditions, same operator and short time.

Repeatability Explained

It is found by applying the same value several times, approaching from the same direction. It is reported as a standard deviation or as the maximum spread.

Poor repeatability points to friction, noise, loose connections or a failing sensor.

Repeatability Formula

s = √[Σ (x_i − x̄)² ÷ (n − 1)]

x_i	individual readings
x̄	mean
n	number of readings

Example: Readings 10.02, 10.04, 10.03, 10.05, 10.01: mean 10.03, s ≈ 0.016.

Calculators for Repeatability

CalculatorRepeatability CalculatorFree online calculator with formula and worked example.CalculatorMeasurement Uncertainty CalculatorFree online calculator with formula and worked example.

Free Downloads

Free downloadMeasurement Uncertainty Budget Excel SheetFree download in Excel and PDF.

Frequently Asked Questions

What is Repeatability?

Repeatability is the closeness of successive readings of the same input under the same conditions, same operator and short time.

How many readings do I need?

At least 5 to 10 for a useful standard deviation.

Is repeatability in the accuracy spec?

Usually yes, within reference accuracy.

Learn more on the blog

Instrumentation calibration and troubleshooting guide

A practical guide on instrumentationblog.in with more detail on repeatability and how it is applied on real plants.

Read Full Article

More Calibration Terms

Calibration termHysteresisHysteresis is the difference between readings at the same input when approached from below (upscale) and…Calibration termLinearityLinearity is how closely an instrument output follows a straight line between input and output; non…Calibration termZero and Span ErrorZero and span error describe an instrument whose reading is offset at the bottom of the range (zero) or…Calibration termMeasurement UncertaintyMeasurement uncertainty is a quantified range around a result within which the true value is expected to…Calibration termCoverage FactorCoverage factor k multiplies the combined standard uncertainty to give an expanded uncertainty at a…Calibration termTest Uncertainty RatioTest uncertainty ratio compares the tolerance of the instrument under test with the uncertainty of the…

All calibration terms · Full glossary A to Z