Unit comes within X of unit event

When using the "Unit comes within X of unit" event, I can get the unit entering the "region"(triggering unit, entering unit).

But how do I find out which unit it comes within range to?

triggering unit

No. Triggering unit equals to the unit entering the "region" too.

As you are using an event, the unit must either be fixed, pre placed, or a variable.

In either case, you simply use the pre-placed fixed unit, or the variable, as the unit that is "approached".

cata

I'd go with a variable -- set it up beforehand.