Lever 1 , turning about fixed axis A, has two lugs a. Roller b is mounted on the end of lever 2 which turns about fixed axis B . If lever 1 is turned in either direction, one of the lugs a depresses roller b and turns lever 2 . Spring 4 returns lever 2 , and, consequently, lever 1, to the position shown in the drawing.
$142$SL,L$