Take a look, in the graph editor , click the pull down menu where it says f-curve and choose driver mode. Select the driver you want to look at in the lefthand property shelf and then the driver details will show up in the right hand property shelf the actual script is just "var" all this does is call the variable below. Or var*-1 (calls an inverted value from the variable. In this instance the variable should just be the z position of the control. (If i remeber correctly)
