I don’t have a Bathmate (am considering it) but I do water-pump using my Velseal. I am currently sucking out the air ‘manually’. I’m comfortable doing this because I’ve been air-pumping for years and feel I have a good sense of the vacuum (and also can tolerate more than when I started, so I don’t have to be bang on any particular reading). In any case, it occurs to me that the level of water in the tube is actually an indication of the vacuum, is it not? I start with the tube about a third filled with water, and evacuate the air until the water is at the top of the tube. Since the Velseal is already marked for length, I would you think you could calibrate to measure the actual vacuum, if so inclined.
plustwo