*Socialmetrica
periodsSince: startingDate until: endingDate
	| endings subperiodDuration |
	subperiodDuration := (endingDate - startingDate) / self.
	endings := OrderedCollection new.
	endings add: startingDate.
	1 to: self do: [ :i | | ending |
		ending := startingDate + (subperiodDuration * i).
		endings add:  ending.
	].
	^ endings