Well, I would say gravity, but thats before I made a lightbulb vape. I can't believe that shit...I weighed out .1g and put HALF of it in the bulb and started vapin' the stuff. I got high before I even put the second half of the .1g in. I'm not really a lightweight, but that is a great way to conserve. Really cool when you feel the high come on too.

I don't know how conserving gravs are anymore though, seems like I always take 3, which usually ends up being almost as much bud as I would pack in my bowl to get about as high. Gravs are just a good method for when you definitely wan't to get blazed and not waste so much (since the smoke usually isn't wasted)