The value of this field can be Recovery : in this case, the statistics are recalculated for all the records corresponding to the dates within the calculation interval, after a rezeroing previously carried out on these records.
If the value of the field is Incremental, the statistics are recalculated without a rezeroing being carried out. The software then proposes by default as the start date, the first date from which the statistics have not been calculated, but it is also possible to check the box From the last update (of particular use if the task is abandoned for example).