Objects in the real world are usually too big to fit on a sheet of paper full size. Think of an architects drawing of a house, it clearly isn't practical to have a sheet of paper the size of a house! We therefore scale down, or reduce the original dimensions. We do this in terms of ratios, dividing the measurements by the scale.

The picture shows the Vauxhall Mokka. It has a length of 4150 mm and a height of 1530 mm. We can scale it down (reduce it) by twenty times and it will fit on a sheet of A4 paper. (The drawing below isn't actually to a scale of 1:20 however because it depends on the size of your monitor).

When engineers work from drawings, they need to know the scale so they know the real size of the object they are working with. We use the opposite of reduction and call this enlargement . Its simply a matter of multiplying the measurements on the drawing by the scale: