Comparison of the Steel Tape with the Standard Yard.


The steel tape used was one of Chesterman's, 100 feet long. It was
compared with Wurdeman's copy of the standard yard, as follows:

Temperature was 55° Fahr.

The standard yard was brought under the microscopes of the comparator; the
cross-hair of the unmarked microscope was made to bisect the division
marked o, and the cross-hair of the microscope, marked I, was made to
bisect the division marked 36. The reading of microscope I was taken, and
the other microscope was not touched during the experiment. The standard
was then removed and the steel tape brought under the microscopes and
moved along till the division marked 0.1 (feet) was bisected by the
cross-hair of the unmarked microscope. The screw of microscope I was then
turned till its cross-hair bisected the division marked 3.1 (feet), and
the reading of the screw taken. The difference between the original
reading and that of each measurement was noted, care being taken to regard
the direction in which the screw was turned, and this gave the difference
in length between the standard and each succesive portion of the steel
tape in terms of turns of the micrometer-screw.

To find the value of one turn, the cross-hair was moved over a millimeter
scale, and the following were the values obtained:

Turns of screw of microscope I in 1mm--