Twice now I have measured preboil gravity and then post boil and found they are close, but just a bit higher after the boil. All grain, 10 gallons, using a thermopen to check the temperature of my sample. I usually collect about 13 gallons of wort and have around 11+ after 60 minute boil. For example, today I got 1.016 at 180f pre boil (converts to 1.045?) and 1.042 at 70f post boil (1.043?). I am more than happy with my efficiency and all that, but I had thought the gravity would increase as volume decreased during the boil. Any thoughts? Maybe this is within the margin of error considering my instruments.