starrDrag() woes

I am having the hardest time understanding the constrained area for startDrag. I ususally end up just trying random numbers until they work. Say I have a box 200px x 200px, with registration on the top left corner… It’s parent clip is 238px by 225px, and has registration set to the middle horizontally and verticaly. How woudl figure out the correct numbers to constrain this? If anyone knows a good tutorial for this-I would relaly appreciate it.