Don't use this method on proofs.

Draw a circle of the same size as the coin on a piece of paper. Use a compass, not the coin itself. Mark the exact 12 or 6 o'clock point of both sides on the edge of the coin with a fine drawing pen. Transfer the two points on the coin to the circle on paper and wipe the ink off the edge of the coin. Work quickly and the ink will not have dried and will be easy to remove.

If you are good at math or an excel god, you can calculate the angle of the lines between the centre of the circle and the two points on the circle by measuring the distance between the two point on the circle in a straight line (callipers) and using

trigonometry. Otherwise, you can draw the two lines and use a

protractor.

If you are really desperate, create a pie chart with two numbers (x and 360-x) in excel, hold the paper in front of the screen, so that the graph shines through and adjust x by trial and error until the lines on paper match those on the chart. Your die rotation is the value of x. The size of the pie chart is not important.

Peter