Sum together dynamic property

What I’m trying to do:

  • I have a bunch of discarded pieces that’s been dragged to a discard pile (a map window).
  • Each pieces has a corresponding cost in points (a dynamic property).
  • I want to use a Global Key Command or something similar to sum together the points of all the pieces in that map window, and report it to the chat log.

Have the discard as a deck, have the deck count properties, have another piece on the same map use the sum of those properties and a trigger to generate a report in response to the GKC.