Saw this old clock from the early 1900s yesterday and noticed it was running about 15 minutes slow. So far nothing unusual. Then I saw it had a subdial which showed it was running 15 minutes slow. So, why would they have this? To know it was running slow, it would have to know the real time and if it knows that, why doesn’t it display the correct time? It was a cool looking old clock, but this feature made it far more interesting.