Jaap's Mechanical Calculators Page




The Schnellrechner is a simple 7-digit adder which was made by Swift Business Machines Corp. in Hong Kong in the 1960s and up until about 1975. The exact same model was also sold under the name Swift Handy Calculator.

Schnellrechner mechanism
Schnellrechner mechanism, cam wheel
Schnellrechner mechanism, close up
Schnellrechner, base inscription

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.

Subtraction is performed using complementary numbers. Next to the printed digits used for addition, there are small red digits. To subtact a number, first mentally subtract 1 from that number, and then enter the result using the small red digits, including entering leading zeroes for all the columns to the left of the number. For example, to subtract 2 you need to enter the number 0000001. This in effect adds 9999998, which causing the register to roll over to the correct result.

The red lever on the left clears the register.

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.

The Schnellrechner is an almost exact copy of the Addipresto, an Italian adder that was made some time in the 1950s. It even uses plastic of the same light-blue colour for the casing, and red for the stylus and clearing lever.


The Addipresto was apparently patented by Sergio Lanza on 14-06-1956, IT554094, but it is not available in the Espacenet database.


John Wolff shows the Addipresto and the Swift Handy calculator.
John Wolff shows the Schnellrechner with packaging.

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