If you use the driveshaft, get the angle using a finder, most point down towards the rear on a leaf car.
Lets say that number is 7*
Pinion is pointing level... 7 - 0 = 7* down in relation to the DS.
If pinion pointed up 2*, it would have an angle of 5*
Pointed down 2*, would be 9*
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Using the trans output, get the angle x* up or down.
Get the pinion reading.
Get those two numbers equal in opposite directions... If trans is 2* down, you want the pinion 2* up to get in the same plane. Then turn it down whatever number you are looking for. If you wanted 7* down, the pinion would have to be 5* down from level. You'd take the 2* that it would point up to get back to zero since it's point UP, then roll down the other 5 to get your 7 total...