Your maths is incorrect. After 2.5 hours you will have seen 5 Redditch units (00:00 = 1, 00:30 = 2, 01:00 = 3, 01:30 = 4, 02:00 = 5 and then 02:30 = 1). Similarly, 6 Bromsgrove units over 3 hours. (It’s like the old school problem with the number of telegraph poles being one more than the number...