1.1 In October 1992, a new policy on expressing measurement uncertainty was instituted at NIST. This policy is set forth in "Statements of Uncertainty Associated With Measurement Results," Appendix E, NIST Technical Communications Program, Subchapter 4.09 of the Administrative Manual (reproduced as Appendix C of these Guidelines).
1.2 The new NIST policy is based on the approach to expressing uncertainty in measurement recommended by the CIPM in 1981  and the elaboration of that approach given in the Guide to the Expression of Uncertainty in Measurement (hereafter called the Guide), which was prepared by individuals nominated by the BIPM, IEC, ISO, or OIML . The CIPM approach is founded on Recommendation INC-1 (1980) of the Working Group on the Statement of Uncertainties . This group was convened in 1980 by the BIPM as a consequence of a 1977* request by the CIPM that the BIPM study the question of reaching an international consensus on expressing uncertainty in measurement. The request was initiated by then CIPM member and NBS Director, E. Ambler. A 1985* request by the CIPM to ISO asking it to develop a broadly applicable guidance document based on Recommendation INC-1 (1980) led to the development of the Guide. It is at present the most complete reference on the general application of the CIPM approach to expressing measurement uncertainty, and its development is giving further impetus to the worldwide adoption of that approach.
1.3 Although the Guide represents the current international view of how to express uncertainty in measurement based on the CIPM approach, it is a rather lengthy document. We have therefore prepared this Technical Note with the goal of succinctly presenting, in the context of the new NIST policy, those aspects of the Guide that will be of most use to the NIST staff in implementing that policy. We have also included some suggestions that are not contained in the Guide or policy but which we believe are useful. However, none of the guidance given in this Technical Note is to be interpreted as NIST policy unless it is directly quoted from the policy itself. Such cases will be clearly indicated in the text.
1.4 The guidance given in this Technical Note is intended to be applicable to most, if not all, NIST measurement results, including results associated with
- international comparisons of measurement standards,
- basic research,
- applied research and engineering,
- calibrating client measurement standards,
- certifying standard reference materials, and
- generating standard reference data.
Since the Guide itself is intended to be applicable to similar kinds of measurement results, it may be consulted for additional details. Classic expositions of the statistical evaluation of measurement processes are given in references [4-7].