If you have a hot box built. (Insulated plywood box with 4 ceramic light fixtures hooked up to a dimmer switch) You can take your roughed out stave and put it in there "on low" and weigh the stave on a regular basis (every other day or whatever) When it quits losing weight at a certain humidity, you can go ahead and consider it dry enough. My box has one of those home weather stations mounted to it, with the sensor inside. I have a chart attached to the side of my box to give me that number, but I'm not home right now. Personally, I believe that if your humidity is fairly stable, and you bow stops losing weight, you can work on it. If you're worried about the humidity, then throw it back in the box each night.