Setting Pivot Point - Odd Behavior

SnapperTrx

I have an object that is comprised of two objects grouped together. They, in turn are part of a bigger group. I want to pivot the object from one end, and have used 'Set Pivot Point' to move the manipulator widget accordingly. When I use the rotate handle on the manipulator it the object moves correctly, but its very imprecise. I have a duplicate object in another location and I would like them both to be rotated the same number of degrees, but in opposite directions. When I enter a value into the Roate parameter of the properties window, however, the object rotates from a different pivot point, thus making the whole operation useless. Have I missed something? Can anyone offer any pointers or information? Thanks for your help.