[Bruce Edwards]

The angle from the rear of the trans to the front of the rear end should be almost straight with the suspension loaded, the car on the ground. The rear end pinion should be pointed just a few degrees down but darn near straight.
You can check it in the air if you put jack stands on the suspension. Just be careful you do not put it on a part that will move as you let the car down on the stands. Wrong place and they can shoot out from under the car or cause the car to "jump" on the stands and may cause it to fall.