Can anyone provide step-by-step directions for using the VW 210 timing belt gauge to test for proper belt tension?

I understand that the belt goes between the fingers on the base of the tool and the spring-loaded plunger that sticks out of the barrel with the numbers on it.
The Bentley says I need a measurement of "12-13 index marks". How do I achieve that measurement? Where do I start? Are "index marks" the white numbers on the barrel or the black numbers on the handle?
Where do you get those things? UK VW would rather eat sh one tee than sell us one. :?
I got one too and i don't know how it works eiter! it never came with directions! at least it looks good in the tool box! :lol: L.O.L.
so I would like to know how to see it work also?
thanks Duane
I believe you set the knob for the desired tension, basically the metal of the knob will stopat the desired number, then put it on the belt, and tighten the belt until the pointer matches your desired tension. The numbers on the knob are a finer scale for exact tension. At least that's what I did when I borrowed one. Doing the twist test, it was more than 45 degrees, but less than 90.
Thanks to Andrew Belzer, I obtained these operating directions for the tool:

Basically, one turns the knurled knob until its edge aligns with 13 on the index (which apparently is in MM) and puts the tool on the belt. If the sliding marker then lines up with the edge of the knob, you have the 13 the Bentley calls for. If it's less, you tighten the tensioner until it is at the edge. If it disappears inside the handle, the tension is too high and needs to be backed off.
ahhh thanks for that post! now that thing makes since! I feel like a professional now! L.O.L.
thanks Duane