Damn you're impatient...
I have one... use it all the time. Here's what I do...
Make sure the o-ring on the bottom part is on the 10 (10# of force to compress the spring inside)
Slide a tap measure in behind the belt (up n down)
Then in the middle where you can get on it... put the belt holder piece that looks like an upward [ under the belt
Make note of where the belt is (with no tension) on the tape measure
Push up on the belt till the o-ring bottoms out on the upper half of the unit. Check the measurement against the tape measure.
You want 1/4-1/2 inch difference.
Now also, you want the bike on the wheels (don't have the bike's rear end jacked up, UNLESS its a hardtail)
Technically you want rider weight on it as well. But I usually don't and its fine. I just try to get 3/8" freeplay.