Make your own Macdonald calculator

You will need:

1. 1 sheet of Letter or A4 paper

2. 2-3 sheets of letter/A4 transparency paper suitable for your printer

3. 1 push pin. 3 more pins, optional

4. Letter or A4 sized piece of foam board

5. 2 pieces of masking tape, optional

6. glue, scissors

Steps

1. Download the PDF below

2. Print page 2 (the disk) on A4 or letter sized paper.

3. Print page 3 (Vernier cursor) and 4 or 5(Index) on transparency. You may later want to print page 5 (Index as a 2nd cursor) and try that out.

4. Glue the disk page (2) to the foam board.

5. With page 3, cut out the vernier cursor shape, also

6. Cut out each of the arrow circles on page 3.

7. Cut out the index ring on page 4.

8. Use a pin to push a hole in the center of the disk, index, vernier, and each arrow, as well as the circles on the bottom of page 2.

9. Assemble the slide rule by stacking the vernier over the index on the disk and insert a pin through the center of all three.

10. Put pins on the arrows and stick those over the circles on the bottom of page 2.

The patent describes having the vernier under a rigid transparent plastic window. This along with the casement (a plan view of it shown on the vernier page 3), and with the index as a rigid ring, would have made a pretty good looking calculator.

Small deviations from the patent:

This calculator doesn't have the 3-dimensional features related to the vernier cursor and the index ring. I represented the vernier and index by transparent sheets, to better accommodate a home build.

Also, I provided center 'holes' on the disk to provide a needed pivot point. The inventor's design did not require a centre hole in the disk.

Because I replaced the ring with a sheet of transparency I was able to add a radial line from the index to the centre of the disk. I find makes it easier to align the index against the cursor and other lines.