As log a rolls to the left it turns lever 1 counterclockwise about fixed axis A. This raises slider 2, forcing yoke d of lever 3 to the left so that pawl 4 turns ratchet wheel 5 counterclockwise. Wheel 5 is rigidly attached to gear b which meshes with gear 6. The rotation of gear b is indicated on scale f by meshing gears 6 and 7 and hand e. Spring 8 returns lever 3 to its initial position.
$1846$LR,FD$