This model is the simplest and cheapest one. It is a hand model which belongs to the first family of calculators the name of which was “Madas Portable”, made from the year 1931. Situated above the keyboard and constructed to move both to the left and to the right relative to the body of the machine is the Carriage. This carries two registers: the upper register extending the full length of the carriage is the Product Register (or Accumulator), which displays the results of additions, subtractions, and multiplications performed by the machine. Its capacity is 12 digits. On the other models, its capacity is twice that of the keyboard. It is called “Register I”.
Immediately below the right-hand half of the “Product Register”, there is a second register, the “Counting Quotient” or “Revolutions Register”. Its main function is to record the number of additions or subtractions made in an operation and to display the quotient in division. Generally, on all models of Madas, its capacity is that of the keyboard, but on the model 12 and 12e, it is only 6 digits. It is called Register II.
Above the topmost row of keys, a special “Setting Register” is provided to see at a glance the number set on the keyboard, as soon as a key is depressed. It is called Register III.
Multiplication is performed by means of a sequence of repeated additions and carriage shifts, while Division is performed by means of a sequence of repeated subtractions and carriage shifts. A distinctive characteristic of the Madas 12 and Madas 12e is that the Dividend must be introduced from the third range of keys of the keayboard, on the left. Moreover, there is no bell for warning (as it is on the models 16, 16e, 20 and 20e), when the Product Register becomes negative, after an excess subtraction.