Results of measurements and conclusions derived from them constitute much of the technical information produced by the National Institute of Standards and Technology (NIST). In July 1992 the Director of NIST appointed an Ad Hoc Committee on Uncertainty Statements and charged it with recommending a policy on this important topic. The Committee concluded that the CIPM approach could be used to provide quantitative expression of measurement that would satisfy NIST¿s customers¿ requirements. NIST initially published a Technical Note on this issue in Jan. 1993. This 1994 edition addresses the most important questions raised by recipients concerning some of the points it addressed and some it did not. Illustrations.

Results of measurements and conclusions derived from them constitute much of the technical information produced by NIST. It is generally agreed that the usefulness of measurement results, and thus much of the information that we provide as an institution, is to a large extent determined by the quality of the statements of uncertainty that accompany them. For example, only if quantitative and thoroughly documented statements of uncertainty accompany the results of NIST calibrations can the users of our calibration services establish their level of traceability to the U.S. standards of measurement maintained at NIST.

Reports NIST research and development in the physical and engineering sciences in which the Institute is active. These include physics, chemistry, engineering, mathematics, and computer sciences. Emphasis on measurement methodology and the basic technology underlying standardization.

This handbook is a both a description of the current practice at the National Institute of Standards and Technology, and a compilation of the theory and lore of gauge block calibration. Most of the chapters are nearly self-contained so that the interested reader can, for example, get information on the cleaning and handling of gauge blocks without having to read the chapters on measurement schemes or process control, etc. This partitioning of the material has led to some unavoidable repetition of material between chapters. The basic structure of the handbook is from the theoretical to the practical. Chapter 1: basic concepts and definitions of length and units; Chapter 2: history of gauge blocks, appropriate definitions and a discussion of pertinent national and international standards; Chapter 3: physical characteristics of gauge blocks, including thermal, mechanical and optical properties; Chapter 4: a description of statistical process control (SPC) and measurement assurance (MA) concepts; and Chapters 5 and 6: details of the mechanical comparisons and interferometric techniques used for gauge block calibrations. Full discussions of the related uncertainties and corrections are included. Finally, the appendices cover in more detail some important topics in metrology and gauge block calibration.