This section is all about the terminology you use to talk about the data you gather, crunch and polish. We'll be looking at the units of measurement you use with data. When you're describing the movement of a particular variable over time, it's essential that you have a good grasp of the measurement units involved. Often, you'll have a choice to make over the measure that you use.

This may on the face of it seem obvious, but are you sure about the difference between money and real values? Nominal and real data? Seasonally adjusted and non-seasonally adjusted? All these terms can make an enormous difference in the interpretation of the data.

Let's look at an illustration of some of the choices you face.