This strain gauge consists of two parts, I and II , connected together by thin flat steel reeds a. Parts I and II have points b and c whose centre-to-centre distance l is the length being measured on the piece being tested. Upon a change in length of the test piece, lever 1, turning about pin 0 (rigidly secured in part II of the strain gauge), turns screw device 2 about its axis, thereby turning hand 3.
$475$SL,M$