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You could talk about the tiny quartz crystal and the piezoelectric effect used to provide a stable time base for the electronic movement.
You could describe the atomic workings of the quartz oscillator and how it resonates at a specific and highly stable frequency, and how this is used to accurately pace a timekeeping mechanism.
And you have to check to make sure he touches the edge at the end of each lap.
Without these observations you cannot be sure that the time is valid.
A swimming race illustrates the simple principles involved in measuring time.
This swimmer is competing in a 1,500 metre race and we have an accurate, calibrated wristwatch.
That is why you need at least two, sometimes three judges to measure the time of the race to the standard needed to enter the record books.
The problem, says Bronk Ramsey, is that tree rings provide a direct record that only goes as far back as about 14,000 years.
The technique hinges on carbon-14, a radioactive isotope of the element that, unlike other more stable forms of carbon, decays away at a steady rate.
Organisms capture a certain amount of carbon-14 from the atmosphere when they are alive.
We note that at the instant the swimmer touches the edge of the pool our wristwatch reads and 53 seconds.
How long has the competitor taken to swim the 1,500 metre race?
Marine records, such as corals, have been used to push farther back in time, but these are less robust because levels of carbon-14 in the atmosphere and the ocean are not identical and tend shift with changes in ocean circulation.