The pinwheel of Odhner (Baldwin)
The casing of most of the Odhner pinwheels calculators present a semi cylindrical part with graduated slide slots. The setting levers which are part of the moveable disk of the Odhner wheels project beyond the slots of the casing. When a lever is positionned on a digit, a corresponding number of teeth protude from the circumference of the wheel. The animation shows how the red teeth protude or disappear in the circumference depending upon direction of rotation.
After setting a number, a full cranck turn (or a motor cycle) rotates the Odhner wheel that meshes with the accumulator gear and force them to progress with the number of digits corresponding to the setting lever position.
The setting levers rotate with the wheels. It is then not possible to check the number one has set during an operation. To improve the comfort a display can be added (generally above the setting levers) to check the input numbers. The dials of this display are automatically freezed when the cranck (the motor) operates. It is then possible to check the numbers we are working with during the operation.
Some calculators with this type of setting levers (in circulars slots), have a special mechanism which keeps the levers in their position during the rotation of the Odhner wheels. Such a mechanism allows to check the numbers during the calculation. Nevertheless the reading is difficult for the reason that the digits are not on a straight line as in the display case.
Some "modern" calculators with keyboard input are pinwheels calculators.