|"I just bought a Master addiator , made in
Belgium. I don't have an image of it, but a similar one is in Pisa. Only the color
scheme is different. If you look at the picture, you'll see 2 "frog's eyes" at
the rear. One is red, the other is green and they contain light bulbs! The machine has an
old type battery (graphite stick, cardboard shell) and some wires disappearing in the
My guess is that the red light warns for not proper carrying tens. There is no set of slides for subtraction, so the lights can not be used for indicating negative numbers (which was my first assumption). I tested the electric connections of the Master 'electric' addiator It works a bit different as expected. I thought the red light would indicate 'forgotten carries' but instead it indicates when to shift the slide up.
The slides are made of two electrically isolated parts: the
lower part is unpainted, as usual, and is connected to the green light; the upper part is
red, and is connected to the red light. Putting the stylus in one of the holes connects
one of the slide parts with the body of the machine, and thereby closes one of the
circuits. IMHO it is quite useless: the paint on the slides already indicates the shifting
direction, and you are already looking at the slide when selecting a digit. So why bother
looking at the lights first ?
At first I used a wooden toothpick as a stylus (the machine
is missing the original one) and I expected that only sliding the slides completely down
would cause the red light to burn. That's why I initially thought the connections were
Zeroing is done by a very robust two-gear crank system. The
machine has a nice alligator-like surface. The crinkles are not just painted, in some
places they are actually pressed in the metal. The machine weighs about 3 kg, has rubber
feet and is surely intended for desktop use.
Photo Source: http://www.df.unipi.it/museo/calcolat/mnsc.html