Calibration Measurement Uncertainty Calculator
Build a simple uncertainty budget for a calibration point. Repeat readings give the Type A term; the reference standard, instrument resolution and any other known limits give Type B terms.
- Type A: u = s ÷ √n = 0.0114 ÷ √5 = 0.0051
- Type B: reference U/2, resolution ÷ (2√3), other ÷ √3
- uc = √(Σu²) = 0.00823, U = 2 uc = ± 0.0165
Uncertainty budget
| Source | Type | Distribution | Standard uncertainty |
|---|---|---|---|
| Repeatability | A | Normal | 0.0051 |
| Reference standard | B | Normal (k = 2) | 0.005 |
| Resolution | B | Rectangular | 0.00289 |
| Other | B | Rectangular | 0.00289 |
GUM Uncertainty Method (Simplified)
uref = Uref ÷ 2, ures = resolution ÷ (2√3), urect = a ÷ √3
uc = √(Σui²), U = k × uc
This assumes uncorrelated inputs with sensitivity coefficients of 1, which suits most direct comparisons. k = 2 gives about 95 % coverage.
Worked example
Five readings with s = 0.0114, a reference U of 0.01, resolution 0.01 and another ± 0.005 limit give uc ≈ 0.0082 and U ≈ ± 0.016.
Frequently Asked Questions
What is Type A uncertainty?
Uncertainty evaluated statistically from repeated measurements, usually the standard deviation of the mean.
What is Type B uncertainty?
Uncertainty from other information, such as calibration certificates, specifications and resolution, converted to a standard uncertainty.
Why divide by √3?
For a rectangular distribution with half width a, the standard deviation is a ÷ √3.
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