1) Make a trigger with the event
Player 1 selects a unit
2) Make an event for that trigger that uses the action 'Game - Display message to all players'
3) Set the message equal to 'convert integer to string' and use the integer of the triggering unit's combat #
4) Assign different targets allowed to different unit and place the units on the map.
5) Select various units and see what patterns you notice.
I'll circle back later and do the same and share my findings.