Measurement error and accuracy class calculator

During calibration, an instrument is compared with a reference: absolute, relative, and reduced error are calculated, and checked against its accuracy class. Enter the instrument reading, the reference value, and the span — the calculator computes all three errors and gives a verdict.

The band around zero is the accuracy-class tolerance; the mark is the instrument's reduced error. The instrument passes as long as the mark stays inside the band.

Input data

Instrument reading Reference (true value) Span, XnSpan — the basis for the reduced error, usually the scale's upper limit. For a 0–10 bar gauge, for example, that's 10 bar. usually the upper limit of the measurement range Instrument accuracy classAccuracy class — the allowed reduced error, in percent, printed on the instrument's dial (0.5, 1.0, 1.5…). The instrument passes if its error doesn't exceed the class. allowed reduced error, %: 0.1 / 0.25 / 0.5 / 1.0 / 1.5 %

Result

Reduced error, γReduced error — error relative to the whole scale, not the current reading. This is what's compared with the accuracy class. — %

Fill in the fields — the verdict will appear here

Absolute error, Δ —

Relative error, δ — %

Allowed by class — %

A green result means the reduced error is within the accuracy class (instrument passes); red means it's exceeded (reject / needs adjustment). The sign of Δ shows direction: “+” means the instrument reads high, “−” means it reads low.

How it's calculated

Absolute error is the difference between the instrument's reading and the true value. Its sign shows whether the instrument reads high or low.
Relative error is calculated from the true value; reduced error from the span — effectively, from the whole scale.
It's the reduced error that's compared with the accuracy class: the instrument passes if it doesn't exceed the class.

Example: An instrument reads 50.4 against a reference of 50 on a scale up to 100 → absolute error 0.4; relative 0.8%; reduced 0.4%. Class 0.5 allows ±0.5% — the instrument passes.

Δ = reading − reference; δ = Δ/reference·100%; γ = Δ/span·100% (span — the normalizing value). The instrument passes if |γ| ≤ the accuracy class. Classes — GOST 8.401-80.

This is an estimate

Verify final values against current standards, the project design, and equipment nameplates.

Explained in the article Метрология: поверка, погрешность, Госреестр

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