What it does:
The 3 different collectors generate these score entries:
1. Difference between score entries in 2 different metrics related by a common identifier, either on your existing scorecard or on another scorecard owned by you. A usecase for this collector is if you were storing a start time and and end time for a particular event (identified by a unique id that would be "stamped" on the start and end times), and you wanted to store the time difference.
2. From existing raw score entries in the current or another scorecard. A usecase for this collector is if had 2 scorecards (call these "child" scorecards) with distinct users on each scorecard and you wanted to create a 3rd scorecard (call this the "parent" scorecard) that combined both sets of users. You would pull data from the two child scorecards into the parent scorecard. Another usecase is when you wish to calculate the difference in the score of one metric from this week's score and last week's score.
3. From scorecard bulletin data in the current or another scorecard. A usecase is if you want to use the previous week's total score vaues in this week's score calculations.