# Jaap's Mechanical Calculators Page

The Addimat is a simple 7-digit adder which was made in Italy from the mid 1950s until the late 1960s.

A 7 digit register is visible in a row of round window holes along the top of the machine. Below this are seven vertical slots, partially exposing the rims of the seven number wheels inside. The numbers 1 to 9 are printed next to the slots. The machine comes with a stylus, and when it is placed in the slot next to a printed digit and then moved down to the bottom, the chosen digit is added at that place in the register. When a digit exceeds 9, the wheel to the left is automatically incremented. To add a sequence of numbers, simply enter the numbers one at a time and the register will show the total.

The red lever on the left clears the register.

It seems that in the USA the machine was sold under the name Addipresto. In Europe the name was changed from Addimat to Addipresto in around 1964.

The mechanism is fairly simple. Each number wheel is also a cam wheel, and pushes back on a spring-loaded carry ratchet that engages with the next wheel. Just after the digit 9 the cam track drops back causing the ratchet to be released and push the next wheel up. This system is reused for the clearing mechanism. When the red lever is pulled, all the ratchets are lifted from the wheels, but the arms of the carry ratchet still push back on the cam wheels, causing them to return to zero.

## Schnellrechner

The Schnellrechner is an exact copy of the later versions of the Addipresto. It even uses plastic of the same light-blue colour for the casing, and red for the stylus and clearing lever. It was made by Swift Business Machines Corp. in Hong Kong in the 1960s and up until about 1975. The same model was also sold under the name Swift Handy Calculator.

Apart from the extra hole on the top right for the stylus, the only real difference between this machine and the Addimat above is that it has a set of complemetary digits next to the slots to aid with subtraction. To subtract a number, enter it using the small red complementary digits, including entering leading zeroes for all the columns to the left of the number. Then add an extra 1 (normal digits). For example, to subtract 2 you need to enter the number 0000002 in red digits and add 1. This in effect adds 9999997+1=9999998, which causes the register to roll over to the correct result.

## Patents

The Addipresto was apparently patented by Sergio Lanza on 14-06-1956, IT554094, but it is not available in the Espacenet database.
A very similar machine was however patented by an Italian more than half a century earlier:

PatentFiling datePublished dateNameDescription
GB 1899/0448901-03-189901-07-1899Carlo Fossa-ManciniAn Improved Adding Apparatus