Once upon a time, when I was older than five but no older than seven, I was sitting on a swing. I was in the moment and listening to the beat of the swing and the beat went on. Yes, the beat went on. As I sat and listened to the beat, I decided to change it. Maybe to something faster, maybe to something slower. I did not really care. Perhaps if I swung lower, it would go faster because I did not have as far to go between ends? So I swung lower and the beat went on. Yes, the beat went on. How about higher. The higher I go, the faster I go. I swung higher and the beat went on. Yes, the beat went on. I experimented more and more. Higher and higher as high as I could go. Lower and lower until the swinging was barely perceptible. And the beat went on.
And it is true. Given a weight and a length, a pendulum will keep the same time no mater how high or low it is swinging. There are subtleties. Pumping action is achieved by changing the weight a little bit in a way that changes the timing a little, but my equipment at the time was insufficiently accurate to detect this.
