Hamann Manus modell C, variant 2
This is really a fantastic machine. Many an amateur has accidentally taken it apart, and subsequently never succeeded in putting it back together. These machines are so alien to the afficcionado of pinwheel calculators that making this mistake is easy. The operating principle is completely different, using geared sectors instead of pinwheels, as later copied by Marchant.The result is that the machine operates very lightly, and also that its use is different from the average Odhner calculator. Whether a number is added or subtracted is dependent on the position of the carriage - which is adjusted by a knob on the base, under the main crank handle. The main crank is only turned clockwise, never counterclockwise. There is a button with an arrow on top of the machine, which allows to either reset or leave the (spring-loaded) input as the crank is turned, making for easy additions as well as multiplications. The carriage can only be cleared when it is in the leftmost position, and there is an automatic division implemented. It works in such a way that you set the dividend in the carriage with the direct entry wheels, the divisor in the input register, to the right of the red dot thoughtfully provided for this exact purpose, and shift the carriage all the way to the right. Now push back the button at the front of the carriage and start cranking - any direction switches and carriage shifts are carried out automatically. There are also some funny interlocks, you can e.g. not get the carriage out of its leftmost position without actually performing a clearing of the result register - to prevent error, but it can lead to annoying mistakes.
My machine has the plastic button on the carriage shift button near the main crank, and the plastic button on the input clearing knob as well - for the latter feaure, it must be one of the very first. They used to be metal, and the plastic ones are nearly always missing. The Hamann-Manus C also has a mysterious lever sticking out to the front, which fold back with the carriage in the rightmost position. This is nothing more than a transport/storage lock with the machine in its most compact form. What it doesn't do is release the tension on the carriage spring though.
