Type B Uncertainty

Type B Uncertainty is measurement uncertainty evaluated by means OTHER than statistical analysis of observations — determined from calibration certificates, manufacturer specifications, published data, engineering judgment, or theoretical analysis rather than from repeated measurement data.

Type B Sources

• Calibration Certificate: Uncertainty stated on the reference standard's certificate — inherited from the calibration lab.
• Manufacturer Specifications: Gage accuracy, resolution, and environmental sensitivity specifications.
• Environmental: Temperature coefficient × temperature variation — estimated, not measured.
• Distribution: May be rectangular (uniform), triangular, or normal — the assumed distribution affects the standard uncertainty calculation.

Why It Matters

• Complete Picture: Type B captures systematic uncertainties that repeated measurements cannot reveal — e.g., calibration bias.
• Rectangular Distribution: For uniform distributions: $u_B = a / \sqrt{3}$ where $a$ is the half-width of the distribution.
• Combined: Type B uncertainties are combined with Type A using RSS — treated identically in the uncertainty budget.

Type B Uncertainty is uncertainty from knowledge — measurement uncertainty estimated from specifications, certificates, and engineering judgment rather than statistical data.