1. Is efficiency based on pre-boil gravity, or post boil? Seems to me it should be pre-boil as you are measuring your extraction of sugars from the grain, but maybe I am wrong.
2. Yesterday, I brewed a batch of Janet's Brown. I hit my pre-boil graivty right on the expected, 1.055 with 7.5 gals in the kettle. Problem is that my (post-boil) OG measured came in at 1.062 vs the expected 1.068. To add to my frustration, I ended up with only 5.25 gals as opposed to the 5.5 gals I was expecting. When I realized I was short on volume, I expected that my OG might come in higher, but that wasn't the case. Anyone have any ideas on this?