When we have more than one uncertainty to deal with, we need to choose which one to take into account for our final answer. To do this, we use the value that has the greatest percentage uncertainty.

The percentage uncertainty is expressed as a percentage whereas the absolute uncertainty is written as a number.

There are three types of uncertainty we need to consider for Higher Physics:

• Reading; occurs when taking a measurement visually
• Random; the subtle differences between experiments that produce differing results are caused by random errors
• and Systematic; when there is something wrong with the equipment or the way in which it is used.

We can limit the effect of random errors by carrying out repeated measurments. You need to know how to calculate the mean and the error in the mean (approximate random uncertainty).