Among the gifts the ancient Greeks bestowed on civilization, the familiar circular clock face and the hour, minute and second system of measuring time are among the most important. Hipparchus and other astronomers of the time divided the hour into 60 minutes – a relationship that makes it easy for modern scientists, engineers and race timers to convert minutes into fractions of an hour. You have to do a tiny bit of extra math if you want to express the fraction in hundredths, which is usually more useful than a raw fraction.

Because the number of minutes in an hour is fixed at 60, you can convert any number of minutes into a fraction of an hour by dividing it by 60. For example, 10 minutes is 10/60 = 1/6 of an hour, and 24 minutes is 24/60 = 6/15 of an hour. It's a good idea to simplify fractions as is done in these examples to make subsequent calculations with the fraction less cumbersome.

Numbers like 1/6 and 6/15 of an hour may be accurate, but they aren't always easy to compare with other time measurements. Converting to hundredths of an hour makes the number more useful. Digital devices can do this automatically, but if you're measuring time with an analog stopwatch, you may have to do it manually by dividing the denominator of the fraction into the numerator to convert to decimal form.

In the first of the above examples, for 1/6 hour, we divide 6 into 1 to get 0.167, giving the result that 10 minutes is equivalent to – rounding to two figures – 0.17 hours. Similarly, 24 minutes or 6/15 of an hour is equivalent to 0.40 hours.

If you have a large number of time measurements to convert and you're in a hurry, you can find conversion charts online to make the job easier.