Cam belt sounds tight but isn't (but it looks like it was)

[pug306driver]

So, not having the "seems" unit, how tight is the belt and whats the rule of thumb??

If a small clamp affair was made to clip onto the belt mid run between cam and hp pump, a clip of known length, and a spring gauge ( like a fishing spring gauge to weigh fish?? ) used, how many pounds to deflect the belt say 45degrees, or would that be toooo much deflection??

I would imaging the correct tension would be to illuminate most if not all up and down "play" in the belt mid run??