Tie-rod 1 is secured to fixed point A. Force P, applied to tie-rod 2, brings links 4 and 5 closer together since rollers 3 are forced to roll down inclined surfaces a. This compresses spring 6. The displacement of link 4 is transmitted by rack b to pinion 7 whose hand indicates the magnitude of applied force P. When tie-rod 2 is released, spring 6 returns links 4 and 5 to their initial positions.
$2190$WL,M$