Common language in the industries we work with associate the words “precision” and “measurement” as two halves of a single phrase. However, early measurement was anything but precise.

In the Beginning
Beginning in pre-historic times, humans began to use parts of the body to estimate dimensions. By about 6000 B.C., several of these had evolved.

These include the Inch: the width of a thumb, Hand: width of four fingers where they join the hand, Span: width of a fully spread hand from thumb to small finger, Foot: length of a person’s (or the current King’s) foot, Cubit: length from elbow to finger tips, Yard: tip of the nose to end of the fully extended arm, and Fathom: two yards.

Through the later part of the 18th Century these “standards” were adequate. Tools and other manufactured items were made by hand, one at a time, and a fraction of an inch one way or the other made little difference.

Interchangeable Parts and Mass Production
At the beginning of the 19th Century, precise measurements became vastly more important. This change was due to Eli Whitney’s idea of mass production based on interchangeable parts. In 1800, he successfully applied his theories to the manufacture of muskets for the U.S. Government.

However, mass production demands precision measuring because each part made for a product must be interchangeable. Uniformity can only be assured and controlled through each operation by accurate measurement. Since all parts of a mass-produced product must be interchangeable from one assembly to another, precision measuring based on set standards is essential.

Throughout the 19th century mass production of all types of goods increased tremendously. In addition to better measuring tools, greater use of mechanically powered machine tools instead of hand tools played a large part in this change.

In the early part of this period, effective mass production was limited by both the speed of the process and the ability of measuring tools to provide accurate and repeatable results. Machines and measuring tools approaching the accuracy of modern standards were not developed until well after the American Civil War.

The Improved Micrometer from Starrett
One very important measuring tool that was precise enough to accelerate the evolution of truly interchangeable parts was the first modern micrometer, patented by our founder, Leroy S. Starrett. Though crude micrometers existed earlier in the 19th century, the new Starrett tool included more precise threads, a smaller head, a locking device, a speeder, and perhaps most importantly, a vernier scale.

The Starrett micrometer and the overall improved accuracy of other available measuring tools, combined with better machinery to rapidly increase the efficiency of mass production in the early 20th century.

One of the most notable examples is Henry Ford's application of these principles to automobile manufacturing. The result was radical price decrease so automobiles evolved from a plaything of the very wealthy to a widely available product in just a few short years.

Modern Definitions of the Yard and the Meter
Two units of measurement, the British yard and the meter, were formerly defined by the Weights and Measures Act of 1878. The yard and its familiar subdivisions of feet and inches, was  more precisely defined as the distance between lines inscribed on two gold plugs in a bronze bar when taken at a specified room temperature. A prototype of the yard is kept in the National Institute of Standards and Technology in Washington D.C. Today, the late 19th century definition standard is not precise enough. Practical measurements is now defined as the international inch in terms of light waves.

Though utilized only partially in the United States, the meter/metric system is the standard system of measurement throughout most of the world. The meter was originally set up to be one ten-millionth part of a meridian running north to south through Paris from the North Pole to the Equator. Eventually, this premise was proved false and over years the international meter has been defined in different ways. Currently the meter equals the distance light travels in a vacuum during 30.663318 cycles of a Cesium atom.

For practical applications such as measuring in a manufacturing environment, the physical relationship was translated by N.I.S.T. using lasers and atomic clocks, then transferred to gage blocks. Gage blocks are the tools that bring these standards of precision to the shop floor.