On the machine I'm currently dealing with, a Kikinda URB-A 1000 (made in Yugoslavia), the way auto downfeed works seems a bit different. There is a dial indicator hanging off to the left of the diamond wheel dresser. The dial indicator is the usual analog type but internally has wiring to react to 3 different situations. Fully extended it lights up the "off" LED, in between in lights up "fine" feed LED and compressed it lights up "roughing" LED.
In other words, you set a long bar that projects from the column such that it is in line with this dial indicator and make adjustments on a micrometer on the bar, plus there are adjustment screws on the dial indicator for when roughing, fine and off occur in the process ! In other words, by "compressed" I don't literally mean fully compressed, but just compressed enough for internals to complete a circuit, and that point is adjustable via a screw on the side of the dial indicator.
The actual mechanism by which the downfeed screw is turned is unclear but it appears to be an electrically activated cylinder of some sort that perhaps pushes on a rack to advance the feed in increments per push. There are two potentiometers on the main panel for "fine and rough grinding allowance".
Sounds weird, but aside from the slight PITA of adjusting that long bar on the column, seems very accurate at least. As the dial indicator is at the wheel dresser, and there is internal lever there, it even automatically compensates for any wheel size deviations resulting from dressing the wheel during the process.
Now the question is, does anyone understand what the heck I just typed ?