If I do decide to turn off the valve during the ride out, I make sure to purge all air out of the line, so the gauge reads zero. At least if you forget, when you look at your gauge pre-splash, it will be clear that it isn't on.Maybe they shouldn't, but they do. Maybe I shouldn't turn the valve back off after setting everything up and checking the SPG, but when there's 40 more minutes to wait before the splash, I often do. This is why you take a couple of deep breaths watching the SPG before you splash -- but you knew this already.