Configures the duration of time within which the amount specified must be reached in order for the milestone to be attained.

In most cases milestones are left as overall which means they the tally is from all available data. However, in some cases you may wish to define a milestone that tracks something in a calendar or fiscal year instead of overall.

For Example
If you wanted to set a milestone that is attained once someone has completed 25 training exercises in a calendar year. The Period would be set to Calendar Year