It shows the average prices for a whole range of goods and services for each month. This is done by a survey done by hundreds of people with clipboards taking notes in shops. The amount of each thing is weighted to reflect the average pattern of expenditure by households. It is based on 1987 = 100.0. So for example the figure for 2003 is 183, which means that prices have gone up by 83 per cent since 1987. The figure for 1921 is about 10, so prices went up times 10 from 1921 to 1987. If you want your wages to go up in line with prices, the relative increase should be about the same.