Measures in the primary curriculum

Exploring time - part 3

Remember do not use a circle to represent a day, because of the association with a 12-hour clock face.

Most people learn to tell the time through everyday situations in which they need to know the time! That’s usually the best way to teach it, not through a separate series of mathematics lessons.

Then there are the added complications related to the variety of watches and clocks that pupils may use, as well as the range of ways of saying the same time. For example, as well as being able to read a conventional dial-clock and a digital display in both 12-hour and 24-hour versions, pupils have to learn that the following all represent the same time of day: twenty to four in the afternoon, 3.40 p.m., 1540 (also written sometimes as 15:40 or 15.40). Incidentally, the colloquial use of, for example, ‘fifteen hundred’ to refer to the time 1500 in the 24-hour system is an unhelpful abuse of mathematical language. It reinforces the misunderstanding, mentioned in Chapter 2, of thinking that ‘00’ is an abbreviation for ‘hundred’. I prefer the BBC World Service convention: ‘The time is fifteen hours.’

A couple of further small points relate to noon and midnight. First, note that ‘a.m.’ and ‘p.m.’ are abbreviations for ante meridian and post meridian, meaning ‘before noon’ and ‘after noon’, respectively. This means that 12 noon is neither a.m. nor p.m. It is just 12 noon. Similarly, 12 o’clock midnight is neither a.m. nor p.m. Then, in the 24-hour system, midnight is the moment when the recorded time of day starts again, so it is not 2400, but 0000, ‘zero hours’. Confused!