I have seen alot of fighting on here when pinion angle comes atleast once a year. And it can be very confusing. I try to make it as simple as I can. Most muscle cars most of us will work on will usually have the rear diff lower then the trans and all we want is the eng/trans centerline paralell with the rear diff/pinion centerline under power but not the same centerline. And most of the time the pinion centerline is lower then the trans centerline as it has been on the muscle cars I worked on so the driveshaft will be lower at the pinion then at the trans which gives some angle to the U-joints so they work and lube themselfs. Just figure if the eng/trans centerline is 0 then on a normal leafspring car that is not raced I would most likely set it about 2 down so when on the gas it should be abbout 0 like the trans and give the driveshaft U-joints the angle they need. But you have to consider the cars suspension and if its a race car as some pinions with the trans at 0 may need to be 4 to 6 down but you have to drive and test the car when done to check for vibration and may have to adjust if the suspension does or does not move the pinion as much as we thought on the gas. Not all cars and trucks will use the same setting but to me you just have to remember you are looking to have the eng/trans and the pinion centerlines the paralell but not the same line as your on the gas. Ron