I am a dope - I couldn’t puzzle out the step measurement so I had to resort to a video.
Interestingly, the video shows another way to use calipers, which is to zero the calipers (fully closed), stick them so the butt end of the slide is flat on the honeycomb bed, and then extend the inner rail down through until it hits bottom.
Edit: ignore this - it’s interesting trivia about calipers but not a good measure for the GF deck height.