Chuck it up in some V blocks and put a dial indicator on it and a degree wheel on the end. Set your marker and dial indicator to zero on the backside of the lobe and start to turn it slowly. Watch until the D.I. hits .050 lift and then note the degree on the marker. Continue to turn until it tops out for lift in inches (do some math with your rocker ratio to find valve lift) turn until the D.I returns to .050 on the backside and then determine the degrees past. You got your duration. Valve centerline is determined from som e lobe centerline, usually around 112-118 degrees from some other point (maybe between the intake and exhaust lobes?) that I dont know. Duration is measured differently from cam manufacturers. Mopar measures them from some weird number, many measure from .050 and some measure from initial valve lift, so you can get a 312 or a 250 from the same cam depending where you start to measure duration. Eg. [Email]250@.050[/Email] is lumpy, and Demon rates their carbs on this cam spec on weather it is a street Demon (lower than 250) or race demon (over 250) performance level. Has to do alot with vacuum requirements. Rollers have a fast ramp rate. Nice for a long duration at a low lift.