Introduction

In the 1930’s a man named Curt Herzstark was developing plans for a hand-held mechanical calculator. In 1938 his progress was stopped for a time when he was forced to create machinery for the German army and was sent to the Buchenwald concentration camp in 1943 where he was allowed to continue to work on his design. After Buchenwald was liberated in April 1945 the first prototype was developed. Since the prototypes 80,000 Type I and 60,000 Type II Curta calculators were manufactured and were phased out in the 1970’s due to electronic calculators.

The Curta was unique for the time for using a single stepped cylinder to drive the whole mechanism, rather than the common solution of having a stepped cylinder for each output register. Because of the Curta having only one stepped cylinder driving the calculator it enables the calculator to do subtraction via the 9’s complement (subtraction through addition). The Type I and Type II Curta’s differ in the number of entry and result registers.

Plans for modification of the original Curta involve changing the stepped cylinder to allow subtraction through subtraction, rather than subtraction through addition. Due to the change in the stepped cylinder that drives the calculator, the addition of a reverse carry mechanism needs to be added to allow numbers to roll back from 0 to 9. The first prototype will be a binary full adder made of Lego.