Member 7 has sharp point a. Rocking prism 2 ends in sharp point b. The distance l between points a and b is the length being measured on piece 1 being tested. Upon a change in length l of test piece 1, prism 2, turning with respect to member 3, moves lever 4 which is linked to prism 2. By adjustment with screw 5, the point of the dial is brought into contact with lever 4. The reading is made on the dial by means of index 6.
$477$SL,M$