Simple, elegant things. Yet somehow very hard to explain. (Also prone to wonderfully spurious precision — less than a second in 138 million years !?) Getting from frequency to time is not necessarily an intuitive thing (also, frequency is a Bad Word). Many years ago, after writing the thing in the first link above, I spent an hour trying to explain it to someone. Working from analogy, getting time from distance travelled a car, was the best I could manage. Pretty sure it didn’t work.