I just push with my thumb what I think is 10 lbs and watch the scale on the guard then give it the 1/4 twist test when done. Works for me

 

While that might be true about the belt failing (I have no idea if it is or not) an over tight belt will stress the seals and bearings more. I'd rather replace a belt than have bearings and seals fail. Both are costly repairs, but I'd rather err on the side of a slightly looser belt. JMHO.

 

The first time I adjusted my drive belt, I tightened to specs. The belt whined once it warmed up. I readjusted letting the deflection decrease about 1/8 of an inch and the problem was solved.

If you use a black sharpie pen and mark the adjustment cam at the right setting it makes it much easier to adjust the belt later. This came in handy after a recent tire change.

 

Changing the shock pressure will change the belt tension. Manual says how much air to put in the shocks before checking the belt at ambient temp, on the side stand with a Harley belt tension gauge in the center of the belt................after several beers!