Hi Alan, if you look at Macolm's explanation again, you'll see that each position that the small circle is in, the letters A, B, C and D are all in the same position, thus for every quarter of roll around the big circle, the same distance has occurred to the circumference to the small circle, which is 3 / 4 of it, but the small circle has rotated once and this happens four times. As I've pointed out, the full circumference of the same circle only makes contact three times. Each of the letters on the small circle will line up with the same letters on the big circle, so when the two A's on the first quarter line up, the small circle has rotated more than once, so you get four times 3 / 4 plus four times 1 / 4.
Regards Nick.
Edited By Nicholas Farr on 11/10/2021 07:44:47