One trick if you've been trying for ages and can't get it "just right".
I start my bike in neutral on the side stand. Let it warm so the idle is smooth as it gets, then put your left hand (no glove) on the actuator arm, now use your right hand to squeeze and release the clutch. You can actually feel through your finger tips the point at which the arm touches the piston in the clutch.
The critical adjustment is critical because you need to make sure when you release the clutch, that feeling is gone, as in the actuator arm isn't touching the piston. I much prefer the touch method to the measurement method, I find it to be much quicker to get right.
PS: This is not a Triumph approved method, but, I did this day 1, the touch method of owning my R3 because the clutch wasn't adjusted right. 8000 miles later, most of it with extra power, not a single clutch issue, still on the original.