Once again...

Set the pinion parallel to the transmission as a base line, then pivot the pinion downward X degrees. X degrees is the pinion angle.

If the transmission slopes downward 2 degrees toward the rear and the pinion slopes upward 2 degrees toward the front (parallel), you have 0 degree pinion angle.

If the transmission slopes downward 2 degrees toward the rear and the pinion is level, you have 2 degree negative pinion angle.

If the transmission slopes downward 2 degrees toward the rear and the pinion slopes downward 2 degrees toward the front, you have 4 degree negative pinion angle.