Objects of Engineering: The standard bars that helped measure to one-millionth of an inch

In the 1840s Sir Joseph Whitworth invented a machine capable of measuring to one millionth of an inch by comparing the end measure of an object against a known standard.

The standard end measure bars were vital elements of this method of measurement. A standard bar would be placed between the measuring machine’s two adjustable sliding bars, each with a measuring plane. The plane ends of the standard bar were required to be truly parallel to the measuring plane. The standard bar would set the standard that later measurements would be made against.

A set of standard end measure bars is held within the Institution’s artefact collection. Our collection of six standard bars ranges between 25mm and 200mm.

Images can be viewed in the Virtual Archive.

Explore the history of engineering and find out more about the IMechE archives here.