NIST Reference on
Constants, Units and Uncertainty
Essentials of expressing measurement uncertainty.
On this page I found NIST Technical Note 1297 (TN 1297), prepared by B. N. Taylor and C. E. Kuyatt and entitled Guidelines for Evaluating and Expressing the Uncertainty of NIST Measurement Results. TN 1297
American Association for Laboratory Accreditation (A2LA)
National Quality Assurance (NQA)
National Association for Proficiency Testing (NAPT)
Single Measurment Uncertanty
I found this on Agilent web page at Helpful Resources "EA-4/02 Released in December 1999, this is a comprehensive (79 pages) and authoritative publication (from Europe's official accreditation organisation). Other than price (FREE), what makes this especially valuable is the number of examples that are used to illustrate the uncertainty budgeting process."
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EA-4/02 Expression of the Uncertainty of Measurement in Calibration