Not really rambling David, a base 10 scale over a 15 second range would allow 40 bpm to be measured, making it more useful to an athlete aiming for that sort of rate rather than the 60+ of us mortals!

15 counts is the norm, and what you assume if no base is specified, but it does vary. If you look at the 1153 Carrera in that section, you'll see it is Base 30. The upshot of that is its 60 bpm mark is at 6 o'clock rather than the 3 o'clock of the 2447 P and the combo scales. Base 30 is more precise but it does run more risk of the very human failing of forgetting how many you have counted!!