Start with the C at the centre of the diagram and follow 2 sequences of letters, both clockwise from the C, one around the upper half of the diagram, and one around the lower half. Letters in the upper half advance through the alphabet in steps of 7 letters at a time, and letters in the lower half advance in steps of 9.

Start on the upper left of each diagram, and move to the right, then down the last 2 boxes in the centre. Letters are written in alphabetical order, in steps of 5 for the left hand diagram, 6 for the next, then 7, then 8.