Dan + Speedy, yes I do have the Audio One, but frankly would have bought the $30 version had I known about it at the time. The little "stylus shelf" shouldn't really be necessary if you just position the scale next to the edge of the platter and support it on something rigid so the measuring surface is even with the top of the platter.
As for accuracy, I've never had a problem, but because we don't use these things very often (at least I don't) I always check the battery voltage before starting, and calibrate it several times during a measurement session just to make sure that zero stays zero.
Once again, like with SRA and anti-skate, the important thing is to get inside the "design range" better known as the "ballpark" so that you can then fine adjust by ear.
In the case of VTF, it doesn't really matter if your scale is precisely accurate in absolute terms. If your cartridge VTF range is say 1.8 - 2.0 and you have a scale that measures in 100ths gm, then you really need only start with a reading anywhere between 1.85 and 1.95 to be in the "ballpark". So let's say you set your VTF for 1.89gm (so what if it's actually +/- .05 gm?) All you need to do after that is keep track of what you think you hear (write it down!) as you go up or down from the initial setting in .01 gm increments. I think educating one's ears to the sonic subtlties of changes in VTF is a far trickier skill to acquire than most folks think, and takes a lot of practice just to hear the changes, much less know with confidence when the setting is the correct one.
If you're really anal compulsive, and you want the numbers on the tonearm dial to read as close as possible to the actual downforce (while at the same time accounting for slight deviations in your own particular scale) then set the dial to read some known force like 1.5 gm, and then using your scale, patiently adjust the counterweight(s) until the scale reads 1.5 gm. That's as accurate as it's ever likely to get, and plenty accurate for audio, in my ever so humble opinion.
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