Semina operating

The Multiplication

This machine is a half-automatic machine. It means that, for the multiplication, figures are entered, one by one, on the multiplier keyboard, and partial results are displayed on the cumulative Register, by adding the product of this computation (multiplicand multiplied by one digit of the multiplier).

The steps are descibed here, for the multiplication 4869 x 176:

  1. Set the multiplicand on the keyboard, by typing 4,8,6,9 at the right
  2. Make sure that the lever, at left, is on “Add/Mult” and press the “REP” key
  3. As the multiplier has 3 digits, the carriage has to be moved 3 positions to the right, before initiating the computation
  4. Press key “1” on the multiplier keyboard. The carriage is automatically shifted one position to the left and the partial result is displayed
  5. Press key “7” on the multiplier keyboard. Again, the carriage is shifted to the left and the partial result is added to the cumulative Register
  6. Finally, press “6” on the multiplier keyboard. Now the carriage has moved to its home position and the final result is displayed
  7. The final result is 856’944


This video shows the same process with the partial results after successive shifts corresponding to entered figures 1, 7, 6.

Here is the process of the multiplication box:
Suppose that we press the key “3”. The toothed rack moves four teeth at right while the motor starts. On the first cycle, the carriage is moved one position at left and the toothed rack is moved one step at left. For the three subsequent cycles, the multiplicand is added each time to the Result register. During this whole process, several interlocks prevent to activate any other key on the machine. Only when the toothed rack is again at its home position, the key “3” goes back up and the machine is again on hand for other operations.