As a member of Farnham RC for a few years we would occasionally be joined by Russ on our Sunday rides. I had an avocet computer and would ask Russ what speed the group were at. He always got it right give or take a mph. He later told me that he knes from the noise his wee clicker made as it was counting the miles. It was mounted on his wheel and forks and he used it for many s year id guess 😊