I was just thinking about time and light and photography but took the wrong trail.A second is measured as “the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom.” Not knowing anything about hyperfine levels, I was just seriously impressed with the number of transitions per second. And my thinking went like this. Light travels at 299,792,458 meters per second. A thousand times that gives us millimeters per second. So, 299,792,458,000 divided by 9,192,631,770 gives us about 32.6. So light travels 32.6 millimeters in the time it takes a cesium 133 atom to transit between its two hyperfine states. Which just happens to be the diameter of the South African Krugerrand. Which also means that if you look hard enough, time is money.