What I'm doing is probably really simple, but I've only ever tinkered with simple expressions.
I have a bulge effect and I want the centre to follow an object, so I pickwhip the position of the object to the bulge centre, but it needs to go "up" a couple hundred pixels. (say 200) How do I modify JUST the y value of the bulge center?
I could move the anchor point of the object and solve the problem, but I'd rather have this knowledge.