Surveillance test procedures
H W Almer · 1976
Surveillance tests are designed to monitor the values of mass standards between calibrations.T\jo types are described; both consist of comparisons of the weights of an ordered set of mass standards with each other.The differences found are compared with those computed from the reported mass values.Surveillance limits based on the precision of both the calibration and the surveillance test processes are computed.These limits are estimates of the departure of the measured differences from the expected, or predicted, differences as computed from the reported values.A larger change is considered significant.Additional measurements to identify individual weights v/hich have changed are required when a given comparison indicates that the mass of one or more of the weights involved has changed.Buoyancy corrections are used to correct for the difference in the buoyant effect on weights of differing densities.Records document the surveillance test results, and control charts help detect trends.Judgments concerning recalibration can be made based on the constancy of the weights relative to the use requirements.