Scarborough,
Try References Quick Reference in tutorials. In this particular case, $RESPONSE is a reference (relatively small) to a presumably much larger scalar. To change the referant that the reference points to you would dereference in the assignment: $$RESPONSE = 0;
Cheers - L~R
Update: Swapped referant/reference per Abigail-II's comment below
Actually, $RESPONSE is the reference, not $$RESPONSE. As for
the quick reference, that just explains how you use references, it assumes you already know what a reference is.