Lowering units TOTAL health by %

How do I make a trigger that says when a unit enters Playable Map Area, it has its total health (not like 10/20 health, I mean like instead of 20/20, lowered by 50% = 10/10) lowered by a set percent (20%(80% total)), or boosted by a set percent (20% (120% total))??

I'm adding difficulties to this map, and I know it can be done, Enfo has done it, but how do you ?

No wait, I didn't read it right, hold on while I repost.

Use the trigger

Thanks!
I'll try testing, if it works (whoever gets the working one right), I'll give some points (if I can figure out how to).

Okay it works!

Thanks a lot, chuayw2000!

If you tell me how I'll send over 20 points to you :D

Nay, forget about the point thing, I dont mind,.