The Hamann driving mechanism

The accumulator dials of the calculator are actuated by gears in catch with the Hamann mechanism. This mechanism is composed of a wheel toothed internally and outside. This wheel can turn freely compared to a disc interdependent of the driving shaft (in gray on the figure). The movement of the wheel is ordered by a pawl which can swivel around an axis located in its medium (and riveted on the gray disc). A spring maintains the pawl against a track made up of two cams. The first one (salmon color) is a fixed cam and the second one (white color) is part of the input lever. When the calculator is not running, the pawl rests on the fixed cam. Animation shows the various positions the cam of the input lever can take.

The two positions which the pawl can take while swivelling around its axis are illustrated below. It can engage inside the gears forcing it to revolve with him, or disunite of the gear which remains at rest.

When a driving cycle is carried out, the gray disk rotates with the pawl. The pawl rolls on the cams by involving with him the gear wheel until it reaches the shoulder and disengage. At this time, the gears do not turn any more and the pawl finishes its revolution. According to the position chosen for the input lever, the fraction of angle during which the gears will turn will be more or less important. The gears are choosen so that the numeral wheels of the accumulator turn of a quantity equal to the digit facing the linput lever.

On the contrary of most of the Odhner levers, the Hamann setting levers don't move during the calculations.