I put a yellow paint dot on the adjuster screw, right at the beginning of the thread next to the ball.
Screwed the adjuster into the rocker until the yellow dot was just showing at the rocker push rod side.
That to me was "0" thread showing.
Ordered push rods at that length, which gave me 2 turns to set preload on the hydraulic roller lifters.
Don't need that much, but it keeps it in the "range" of 0 to 2 turns.