Rotational laws of physics are applied to the crankshaft, harmonic damper, flywheel, or flexplate, along with the big end of the connecting rod. The piston and companion components, along with the connecting rod (from the mid-point to the small end), are identified as reciprocating. When balanced, the rotational components will posses no heavy areas acting upon the crankshaft, trying to pull it from its axis of rotation. The identification of mass differential is accomplished on a machine such as the Sunnen DCB-750 crankshaft balancer. It is representative of a hard cradle design.