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The National Standards of Length and Mass, U. S. Prototype Meter 27 and U. S. Prototype Kilogram 20, are kept in this Standards Vault. Made of a stable alloy containing 90 percent of platinum and 10 percent of iridium, these standards are basic to all length and weight measurements in the United States. On daily display, the standards are safeguarded by a heavy alarm-protected glass door. View shows final inspection before standards were put on exhibition.


The subject of weights and measures is of universal interest. Millions of daily industrial operations and commercial transactions depend on a uniform and convenient system of weights and measures.

In its broadest sense the subject of weights and measures covers much more than the units used in the sale and purchase of commodities. Our high standard of living depends in large part on our ability to measure accurately everything from a loaded railroad car to the diameter of a submicroscopic particle. In fact, almost everyone makes daily use of an accepted system of measurement from the school child who studies arithmetic to the machinist who measures to a ten-thousandth of an inch, from the housewife who purchases a pound of butter to the manufacturer of automotive engines.

The National Bureau of Standards receives many requests for information. on both the customary and metric systems of weights and measures. It is to serve this need-for teachers, students, and the general public that this Circular has been prepared. It brings together much of the information that was previously available in separate mimeographed leaflets. For scientists and industrialists who want more extensive information on the subject, the Bureau has published Units and Systems of Weights and Measures, Miscellaneous Publication 214.

A. V. ASTIN, Director.



1. Introduction..........

2. Units and systems of weights and measures_

2.1. Origin and early history of units and standards.
a. Units and standards.

b. General survey of early history of weights and measures.
c. Origin and development of some common units.

2.2. The metric system

a. The metric system: definition, origin, and development.

b. Units and standards of the metric system__

c. The International Bureau of Weights and Measures..

d. Present status of the metric system in the United States.
e. Arguments for and against the metric system. -

2.3. British and United States systems of weights and measures.
2.4. Subdivision of units_-_-

2.5. Arithmetical systems of numbers_

3. Standards of length, mass, time, and capacity.

3.1. Standards of length..

a. Tests and calibrations of length standards.

3.2. Standards of mass_

a. Distinction between mass and weight

b. Effect of air buoyancy.

c. Tests of standards of mass

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3.4. Standards of capacity.

3.3. Standards of time. _

a. Tests of standards of capacity

4. Weights and measures in everyday life

4.1. Weight of coal.

3.5. Maintenance and preservation of fundamental standards of length and mass.

4.2. Definitions and usages of the terms "ton" and "tonnage".

a. Definitions and uses of "ton"-

b. Definitions and uses of "tonnage".

5. General tables of weights and measures_

5.1. Tables of United States customary weights and measures. 5.2. Notes on British weights and measures tables

5.3. Tables of metric weights and measures_

5.4. Tables of interrelation of units of measurement5.5. Tables of equivalents.

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Units and Systems of Weights and Measures

Their Origin, Development, and Present Status

Lewis V. Judson

This Circular brings together in a convenient form information about weights and measures that experience has shown is of interest to the general public. Much of it has been issued previously by the National Bureau of Standards in temporary and scattered form. The Circular discusses the origin and early history of units and standards, gives general information about the metric system, and states and explains the present status of standards of length, mass, time, and capacity in the United States and in Great Britain. It discusses for the benefit of the general reader such matters as the distinction between units and standards, and that between mass and weight. Two items of everyday life relating to weights and measures are considered in some detail: The weight of coal, and the definitions and usages of the terms "ton" and "tonnage." The Circular concludes with tables of weights and measures, prepared for the benefit of those requiring such tables for occasional ready reference. School teachers will find in this Circular considerable material to supplement their textbooks.

1. Introduction

The National Bureau of Standards was established by act of Congress in 1901 to serve as a National scientific laboratory in the physical sciences and to provide fundamental measurement standards for science and industry. In carrying out these related functions the Bureau conducts research and development in many fields of physics, mathematics, chemistry, and engineering. At the time of its founding, the Bureau had custody of two primary standardsthe meter bar for length and the kilogram cylinder for mass (or weight). With the phenomenal growth of science and technology over the past half century, the Bureau has become a major research institution concerned not only with everyday weights and measures but also with hundreds of other scientific and engineering standards that have become necessary to the industrial progress of the Nation. Nevertheless, the country still looks to the Bureau for information on the units of weights and measures, particularly their definitions and equivalents. The subject of weights and measures can be treated from several different standpoints. Scientists and engineers are interested in the methods by which precision measurements are made; State weights and measures officials are interested in laws and regulations on the subject and in methods of verifying commercial weighing and measuring devices. But a vastly larger group of people are interested in some general knowledge of the origin and development of weights and measures, of the present status of units and standards, and of miscellaneous facts that will be useful in everyday life. This Circular has been prepared to supply that information on weights and measures that experience has shown to be the common subject of inquiry.

2. Units and Systems of Weights and Measures

The expression "weights and measures" is used in this Circular in its basic sense of referring to measurements such as length, mass, and capacity, thus excluding such topics as electrical measurements and thermometry. This section on units and systems of weights and measures presents some fundamental information to clarify thinking on this subject and to eliminate erroneous and misleading use of terms.


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