My procedure is like this:
I Use a homemade degree wheel, where I marked the cam timing on, ie. 16 and 60. ( See pic)
If you the use the 0,85mm Tom wrote - you should be very close to the correct cam duration (256 degrees)
1. step - find TDC and align your degreewheel to 0 degrees
2. step - find the exact value ( 0,85mm Tom wrote is close) that gives you the cam duration of the actual cam you are measuring on.
I get 0,78 mm and 0,82 depending of the angel from my gauge compared to the valve angel. I can't messure on a 0 degree to the valve - the cam is in the way
3. Step - When you have this, use a removable marker or tape strips to mark your actual degree on opening and closing on the wheel.
Depending on the reference (overtight in my preferable way - as this gives a better feelling, and there is no "slack" in the belts) - and say you will move the timing from the OEM 112 to 107 - mark your degree wheel with 21 and 55 ( 5 degree advance)
4. step - rotate your engine to the new opening point ( 21 degree - remember to rotate the engine same way around as it runs)
5. step - Loosen the 3 screws in the can wheel (Testastretta only) and very gentle rotate the cam to you get the actual lift found under step 2.
6. Step - verify and redo if needed.
7. step - next cam
Good luck
