Theoretically, the number of liftings performed over a period of 15 minutes should be counted (for the observed period to be representative of the task) and then divide that number between 15 in order to calculate the frequency (liftings/minute).

In practice, it is best to calculate the frequency from the production data. For example, in a warehouse 2 workers prepare 20 pallets during their 7-hour workday (450 minutes), and each pallet includes 90 boxes, the average frequency of the two workers will be 4 liftings/minute (20x90/450). Therefore, each worker performs 2 liftings/minute.