THE NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards1 provides measurement and technical information services essential to the efficiency and effectiveness of the work of the Nation's scientists and engineers. The Bureau serves also as a focal point in the Federal Government for assuring maximum application of the physical and engineering sciences to the advancement of technology in industry and commerce. To accomplish this mission, the Bureau is organized into three institutes covering broad program areas of research and services:

THE INSTITUTE FOR BASIC STANDARDS. . . provides the central basis within the United States for a complete and consistent system of physical measurements, coordinates that system with the measurement systems of other nations, and furnishes essential services leading to accurate and uniform physical measurements throughout the Nation's scientific community, industry, and commerce. This Institute comprises a series of divisions, each serving a classical subject matter area:

-Applied Mathematics-Electricity-Metrology-Mechanics-Heat-Atomic Physics-Physical Chemistry-Radiation Physics- Laboratory Astrophysics2-Radio Standards Laboratory, which includes Radio Standards Physics and Radio Standards Engineering-Office of Standard Reference Data.

THE INSTITUTE FOR MATERIALS RESEARCH... conducts materials research and provides associated materials services including mainly reference materials and data on the properties of materials. Beyond its direct interest to the Nation's scientists and engineers, this Institute yields services which are essential to the advancement of technology in industry and commerce. This Institute is organized primarily by technical fields:

-Analytical Chemistry-Metallurgy-Reactor Radiations-Polymers-Inorganic Materials-Cryogenics2-Office of Standard Reference Materials.

THE INSTITUTE FOR APPLIED TECHNOLOGY... provides technical services to promote the use of available technology and to facilitate technological innovation in industry and government. The principal elements of this Institute are:

-Building Research-Electronic Instrumentation-Technical Analysis-Center for Computer Sciences and Technology-Textile and Apparel Technology Center-Office of Weights and Measures -Office of Engineering Standards Services-Office of Invention and Innovation-Office of Vehicle Systems Research-Clearinghouse for Federal Scientific and Technical Information3-Materials Evaluation Laboratory-NBS/GSA Testing Laboratory.

1 Headquarters and Laboratories at Gaithersburg, Maryland, unless otherwise noted; mailing address Washington, D. C., 20234.

2 Located at Boulder, Colorado, 80302.

3 Located at 5285 Port Royal Road, Springfield, Virginia 22151.

Realistic Uncertainties and the

Mass Measurement Process

An Illustrated Review

Paul E. Pontius and Joseph M. Cameron

This paper gives a review of the concepts and operations involved in measuring the mass of an object. The importance of viewing measurement as a production process is emphasized and methods of evaluating process parameters are presented. The use of one of the laboratory's standards as an additional unknown in routine calibration provides an accuracy check and, as time goes on, the basis for precision and accuracy statements.

Key Words: Measurement, measurement process, uncertainty, mass measurement, precision, accuracy, statistical control.

Introduction

This paper is a condensed version of a lecture on "Error of Measurement" presented by Paul E. Pontius and Joseph M. Cameron at the Seminar on Mass Measurement, held at the National Bureau of Standards, Washington, D. C., November 30, December 1 and 2, 1964, and is essentially as presented by Paul E. Pontius at the 20th Annual ISA Conference held at Los Angeles, California, October 4-7, 1965.

It is a review of the mass measurement process from the initial basic concept to the statement of a measured mass value, examining in more or less detail certain important elements which are apt to be misunderstood, or perhaps misused. The importance of viewing measurement as a production process is emphasized and methods of evaluating process parameters are presented. The use of one of the laboratory's standards as an additional unknown in routine calibration provides an accuracy check and, as time goes on, the basis for precision and accuracy statements.

Mass Measurement Requirements

One role of the Bureau is to provide an extension of the mass measurement unit into the facilities of those who must use mass values to do other useful work. . . . These large weights, for example, are for use by another part of the Bureau to calibrate force measuring devices.

The calibration service provides values for single, selected groups, and ordered sets of standards, the values being with reference to the national