Advertised in the forms shown below during the 1920s and 1930s, and similar in design to other high-precision measuring machines made by the likes of Société Genevoise d'Instruments de Physique (SIP) in Switzerland, the P & W Precision Measuring Machine was intended for checking tolerances to within 1/100,000" (0.00001"). The unit was first made available in the 1890s and is shown, near the bottom of this page, in the maker's catalogue for 1889 (highly collectable, these sales publications contain an almost unbelievably wide range of machine tools and measuring and inspection equipment).
Manufactured in a number of models that could measure lengths of 12, 24, 36, 48 and 80 inches, the Precision Measuring Machine and would have been made to virtually the same standard as those supplied to the American Bureau of Standards and as well as similar organisations that existing in all advanced countries. Needless to say, in order to produce accurate results, the machine was best housed in a temperature-controlled and preferably vibration-resistant room and handled only by trained personal.
Like the "Lord Chancellor" microscope designed and built by the famous English engineer Henry Maudsley in the early 19th century - and the subsequent types manufactured by Joseph Whitworth in the 1840s - the bench-mounted "Super Micrometer" by Pratt & Whitney was intended as the final arbiter of standard in a large toolroom.
The catalogues below give a clear description of the two machines with their construction and operation fully described.

The Pratt & Whitney Standard Measuring machine as shown in the maker's catalogue for 1889