squares. Each square has triangular holes cut in it according to the patterns given in the following diagram. So for example the mask strips for the simples 3, 6 and 9 will look as follows: The guide lines in the patterns are for positioning the holes. They do not need to appear on the strips. The main diagonal line of each mask pattern, however, shown here in red, is marked on the mask strip. It is an important part of the device. The pattern given here for the simple 0 is from later editions of Napier's book. The version of the 0 strip in the first edition had no holes in it. Performing a Multiplication Number strips for the first of the numbers to be multiplied, the multiplicand, are placed on the calculating board side by side, running from top to bottom of the board. In the example shown here, the multiplicand is 772. Mask strips for the second number, the multiplier, are placed horizontally on top of the number strips. In the example, the multiplier it 396. The result of the multiplication is read from the device by examining the digits visible through the triangular holes in the mask strips. Those parts of the number strips that are not covered by the mask strips are ignored. The diagonal lines on the mask strips divide the device into diagonal bands containing digits visible through the holes. Starting at the right, the first band with any visible digits contains just one digit, a 2. This is written down as the right-most digit of the result. The next band from the right has three digits, 2, 1 and 8. These are added together to get 11. The units digit of this addition, 1, is written down as the next digit of the multiplication result. The tens digit, which is 1, is carried into the next band. The third band from the right has five digits, 2, 4, 3, 1 and 6 plus the carried 1. These are all added to produce 17. The units digit of this, 7, is written as the next digit of the result. The tens digit, 1, is carried into the next band. This process is repeated for each diagonal band from right to left until all the digits have been processed. The full result has now been written down as 305712. This is the result of multiplying