Before you read on, there is one important thing you must remember. Try doing this activity. Get a trundle wheel and a tape measure to measure a straight line. Compare the results. Are they different? Most likely, yes. Look at the reading of the tape measure more closely. Is the length of the line exactly the same as your measurement? Actually, no. In real life, it is impossible to get the exact value of any form of continuous data.

Measurement itself is a kind of estimation; however, as you probably know how to measure things already, we will not go into detail here. Instead, we will learn some forms of indirect measurement. Indirect measurements requires more than a single tool. We will discuss different strategies of indirect measurement in the two coming chapters.

## Before you startEdit

Ask yourself if you are capable of using the correct apparatus and units to calculate weight, length and capacity. Recall all the formulae related to area you have learnt, and preferably put them down somewhere so you always remember them. The examples in the main text will only cover the simplest formulae, i.e. the areas of squares and rectangles. There will be more difficult formulae in the exercises, however, so you may skip questions which require formulae you don't know.