Ok. It's a good guide. I used it for primary belts too. The time it won't work is on very wide belts like a custom Harley primary but I don't use those. As @West Cork Paul it's not that critical. However, too tight is not good.
Sorry if this sounds pedantic, but i wouldn't call it a good guide either, as it could ruin a belt and even create a dangerous situation. If you want longevity for the belts, and if you want to safeguard your whole engine, i would call it critical. I would agree that it's slightly less critical on a 2 valve Ducati engine than a 4 valve Ducati engine.
Just my musings, I've had the bike for more than 30 years and I can't remember how many times I've changed the belts. So far so good. Also I've never changed belts that "look" like they need changing. The ones I've just replaced look brand new. Personally, I wouldn't change 4 valve belts myself. No I haven't, I've had it for 25 years, it's 30 years old. My advice, if you're in doubt, use the Ducati service tool.
