Made in 1968 by the Selective Educational Equipment Corporation, this piece was used to teach students about early methods of calculation and mathematical tools. In some ways it resembles Blaise Pascal’s machine of 1645.
The device has 4 turning dials each with the digits 0 to 9 inscribed on it and viewable through a small gap at the top of the acrylic frame. This indicates that it is capable of displaying any 4 digit number from 0 to 9999. Each dial is connected to the next with 3 intermediate cogs. On the outer rim of the large cogs there is a raised bar which will be discussed later.
To operate this device one would use a thin stylus or pencil and would turn the dials clockwise to set the first number. This method of rotating numbers to the desired value is very similar to an old rotary dial phone. If addition was being carried out the operator would, dial by dial starting from the units, would select the white number on the outer ring to add. For example if 235 was the number being added, the white 5 would be selected and rotated clockwise on the first dial, the white 3 on the second dial and rotated and the white 2 on the third dial. This method is simple yet effective for adding numbers and can be extended to as many digits as were required by simply extending the board. Now those large raised bars on the outer cogs were used to carry ones from the previous column to the next. For example, 9+1 would leave a 1 in the 10’s column and a 0 in the 1’s. The bar is rotated as the dial rotates and on passing the number 9 to the number 0 rotates the dial to the left one place, effectively carrying a 1 to the next column. The reverse of this in subtraction occurs when moving from a 0 to a 9. Note it is very important to start from the 1’s column the right most and work to the 1000’s column, left. Although this model was made for educational purposes, it represents many similar devices that were popular in the first half of the twentieth century.
This item is part of the UQ Physics Museum Good Old days of Calculation Tour
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