Time is divided up into units. There are:

• 60 seconds in a minute;

• 60 minutes in an hour;

• 24 hours in a day;

• 365 days in a year.

In a leap year, which takes place every 4 years, there are 366 days. The extra day in a leap year is added at the end of February (February 29th). For the rest of this century, leap years happen if the year can be divided by 4.

Months are of varying length: January (31 days); February (28 days, 29 in a leap year); March (31); April (30); May (31); June (30); July (31); August (31); September (30); October (31); November (30) and December (31).

There are 7 days in a week. For calculation purposes, there are 52 weeks in a year.

A day is divided up into AM and PM. Note that 12 noon, or midday, is actually 12pm and that midnight is 12am.

A 24-hour clock has 4 digits (add a leading 0 if necessary: 9.25am becomes 0925). If the time is in the afternoon, add 12 to the hours (3.45pm becomes 1545).

At midnight, the day starts again as 12am (or 0000, in 24-hour clock).