The next step is to calculate the total number of defects
in all the samples and enter it in the box labelled *sum c*. This
total can be calculated in two ways:

- add up the
*c*values for all of the samples, as given in the row labelled 'Defects (c)', or - add up all the frequency values in the column labelled 'f'

In order to check that all your figures are correct, we recommend doing both calculations, and checking to make sure that the results are the same!