What Formula is Fourth using to calculate absence and Turnover %?

I need to confirm what formula fourth is using to calculate absence and turnover % e.g. in the absence analysis report that shows a bradford factor.   We also have two other options (Employee turnover and employee turnover by location) and we need to know how the percentage is calculated (probably is number of leavers/number of employees) but what employee number is taken (1st of the month, average, etc)   @E M​