The Rapid Computer Adding Machine With Box

The Rapid Computer

This is called a Rapid Computer. This particular one was made between 1906 and 1908 in Michigan. Its outer case is made of nickel-plated brass, and it has 9 vertical brass sliders at the top, which you control with a stylus. Further down is a celluloid window showing a 9-digit register, which is a row of 9 number wheels on a common axle. Each slider has the numbers 1 to 9 on them, and to add a number to the register, just put the stylus on the correct digit for a column and slide it down until the stylus hits the stop bar. When you release the slider, it springs back up to its original position, and the corresponding register wheel will have increased by your chosen digit. The register has a carry mechanism, but it can be difficult to execute a carry when several numbers have to roll over because it does not use stored energy.

There is a clearing knob on the right, on the axis of the register. To clear the register you have to pull out the knob slightly to unlock it, and then turn it anti-clockwise almost a full turn. This resets all the number wheels. You must then turn the knob clockwise back to its original position, where it will lock into place. If the knob is not returned, then the register will not correctly perform carries.