[wilf leek]

Ernie - it is essentially making sure that the rear axle drive line is exactly at 90 degrees to the car fore and aft centreline.

Can be difficult to set up - easily confused with toe measurements. Adjusted by adding shims in front of the forward inner wishbone pivot bearing caps, where they tie into the chassis. Have to slack off the four bolts holding the diff in at the top as well. Don't forget to safety wire everything on that rear end. Wishbone pivot carrier bolts, caliper bolts, top diff bolts - all need to be safety wired.