מחשבון אי-ודאות מדידה

Measurement uncertainty quantifies the doubt about a measurement result. It defines a range within which the true value lies with stated probability (typically 95%). Required by ISO 17025 for all labs.

Type A = evaluated by statistical analysis (repeated measurements → standard deviation of mean). Type B = evaluated from other info: calibration certificates, specifications, published data, experience.

k multiplies combined standard uncertainty to give expanded uncertainty. k=2 ≈ 95% confidence. k=3 ≈ 99.7%. k=2 is the default for most calibrations.

For independent sources: RSS (root sum of squares): uc = √(u₁² + u₂² + u₃² + ...). Each source value is first divided by its divisor to get standard uncertainty.

GUM (Guide to the Expression of Uncertainty in Measurement) is the international guide published by JCGM. It is the basis for ISO 17025 uncertainty requirements and provides the framework for evaluating and expressing measurement uncertainty.