Simplified Methods for Calculating Uncertainties for Routine Calibrations

Calculating uncertainties is one of the more time-consuming and sometimes daunting tasks for ISO/IEC 17025 accredited laboratories. However, the emphasis for laboratories, accreditation bodies and their assessor has been on the uncertainty budgets that support the laboratory's Calibration and Measurement Capability (CMC) that is summarized in its Scope of Accreditation. This is a summary of the calibrations the laboratory can perform using its best equipment, conditions and staff. It is difficult for laboratories that intend to be profitable in a competitive environment to invest as much time in the development of the uncertainties for the routine calibrations as they do for the CMCs. The loopholes that some accredited laboratories have used to avoid the effort of calculating uncertainty on a regular basis are being closed due to stricter enforcement by their accreditation bodies and more restrictive clarifying standards such as ILAC P14. This paper offers some practical advice for laboratories seeking to calculate uncertainties in an efficient way for the majority of their calibrations which are not to their tightest uncertainties.