The automatic multiplication

The standard multiplication :

The multiplicator "999" is displayed in the windows of the counter at the bottom left of the screen. The carriage is pushed by hand to the leftmost position and released, then the multiplication starts. We observe a succession of 9 additions for each of the multiplicator digits. Each time an addition is performed, the concerned digit of the multiplicator is decreased by 1. When this digit is null, the carriage moves to the next decimal position to continue the additive cycles.

When the result is obtained, 3 x 9 = 27 additive cycles have been done.

Clic on the control bar to see the movie.

The multiplication with the short cut method :

For the same multiplication as above, this method does only two cycles, the first in addition mode and the second in substraction mode. Firstly, the carriage moves to the right from 3 positions and an addition is performed (at this moment the multiplicand has been multiplied by 1000). Now, the carriage comes back to the unit digit position to perform one substraction. Finaly the multiplicand has been multiplied by 999 = 1000 - 1.