I recently purchases a pair of these for my large and small dillon powder bars. They replace the adjustment bolt (no more 7/16 wrench to change powder settings). The scallops on the edge of the knob provide enough reference points (28) to be able to return to a previous setting. By my calculations, that is enough resolution to return within 0.05 grains for pistol loads and 0.1 grains for rifle loads. A real micrometer (like the uniquetek) would be nice, but not at $50 per powder bar. I had planned to purchase an extra measure, but these work well enough to stay with one measure and just record the adjustments for different loads.
Customer service was good. Here is the main website where you can see other color choices and a diffent style knob. http://home.comcast.net/~videodog/