So I have been brewing since January of this year. I have never brewed a bad beer, and never had an infected batch. Most of the beers I have brewed are big beers(1.080+). And I can definitely tell that they have an abundance of alcohol. But according to my hydrometer readings, I am consistently 20 points low(maybe not always 20 points, I would say at least 10 points and sometimes up to 20). I have bought 3 hyrdrometers and checked and they are all the same. I get my grain milled at my LHBS, and I have never asked but I dont believe that they have problems(but I guess they could). And all my beers finish out at 1.010 or lower. I have used 2 different digital lead thermometers, and tried mercury as well, and as far as I can tell im accurate with my mash temp within a few degrees. I fly sparge with 168-174 degree water. I usually go for whatever pre boil volume beersmith says, but I never get the pre boil gravity that it says i should. Not sure on my setup how much wort I boil off in an hour, I usually just watch it and if its not boiled down enough I will turn up the heat and vice-versa. For a few months I was brewing every Saturday, I would say I have brewed 25-30 times all together. My first batch was a partial mash kit, and from then on its been AG all the way. I hope that's enough information to at least give me a possible scenario, but if not ask anything you need. I keep good notes so I should be able to answer anything. Thanks in advance!