Hassler bought the Troughton Scale in London in 1815 for the United States from the instrument-maker Edward Troughton. It is a graduated line standard of 82 in. The interval between the 27 in and 63 in graduations was selected by Hassler in 1832 to define the United States yard at 62° F. It served as the primary standard of length in this country until about 1857 although Hassler regarded the English Parliamentary Yard of 1758 as the real standard. Hassler used Troughton's Comparing Arrangement to compare the French Meter with the English Yard demarcated on the Troughton Scale for both the Coast Survey work and metrological work.

Follow a path that traces the historical development of length comparators.

Diagram of Troughton's Comparing Arrangement