I have a pretty simple hand rig with only 3 fingers, and I want a controller bone to drive the local X rotation of the entire finger so that an increase in the Z scale of the controller bone increases the X rotation of the finger bone toward the center of the hand,and vice versa. I was able to achieve this for only one of the finger bones using a driver for the X rotation with the expression: var -1. However, this only works for one bone in terms of deforming in the way you would expect the fingers to splay naturally. When copying the driver to another finger bone, I want the X rotation to be mirrored from the working bone. For example, when I decrease the scale of my controller and end up with an X rotation value of -.3 for my one working finger bone, I want the opposite finger bone to have a mirrored value of .3. I can't seem to fix my expression in a way that achieves this.
Screenshots for more clarity:
In short, I want the not working bone to mirror the X rotation of the working bone. Simply changing the expression to var + 1 doesn't really work here. Any suggestions would be appreciated.