The instruction sheet for this thing was a joke. The gauge came prefilled, and the needle was sitting a -6 with no vacuum. I had no idea what to do about it, as I have little experience with pressure pot vacuum gauges... I had to search for zeroing oil filled vacuum gauges to figure it out.I'm giving it 5 stars anyway, because it does work, feels sturdy, has a nice reinforced hose, and will suit my needs just fine (I'm using it for degassing silicone and resin).