Tips for setting VTF on VPI Classic?

Does anyone have any tips for making very small changes to VTF on the VPI Classic? As Classic owners know (and owners of all VPI tonearms), the counterweight is not theaded but slides after a small lock nut is loosened. Sliding it back and forth incrementally is very difficult, or I have at least found it to be difficult-I almost always overshoot in either direction. I imagine anyone who uses the crude Shure guage that comes with the table wouldn't notice, but on my digital scale which I carefully place to be almost exactly level with a record placed on the spindle I find it difficult to dial in a reading of 1.75 grams, my target. No matter how small a change I try to make in sliding the counterweight to or fro, I end up at least .10 grams on either side of my target. FWIW, I am running a Benz Glider which may be part of the problem, being fairly skeletal and light.
The manual refers to placing an allen key in the back of the tonearm wand to make smaller adjustments, turning a weight inside the arm but I have found that to be of no help either. When I turn that weight, the entire tonearm wants to rotate due perhaps to excessive friction/tightness of the internal threads (?). Maybe the interior weight is all the way "in" and I should back it out and start over with the counterweight and then the internal weight? Has anyone else noticed this?
I still LOVE my Classic, and the sound is good at 1.65 grams where I have relunctantly settled for the time being.