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.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.

” You cannot know how long the swimmer took unless you knew the time on the wristwatch when the race started.

Without the starting time it is Actually, knowing the starting time is still not enough.

During the race you have to watch the swimmer and count how many laps he has swum so you know that he has done 1,500 metres.

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.

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?Carbon dating is a way to learn the age of an organism that may be thousands of years old.A chemist named Willard Libby worked out this method of dating in 1949.Since Libby's discovery, scientists have used carbon dating to determine the age of various environmental and archaeological artifacts.Learn what you need to do to find a good sample and date it within a narrow margin.