I have a book about incubation by Katie Thear, I don't know if it's well known, I found it online and it had good reviews. There is a formula in the book for checking the air sac development by weighing the eggs before incubation and at later times, to check that the percentage weight loss is on track. The author says it should be 11-13% by day 19. We are trying dry incubation (having only incubated once before, wet, and it went very badly!) I added a tiny amount of water yesterday as when I weighed the eggs for the third time (day 11, the others were day 0 and day 7) they seemed a little too light. Except for one, which is the same as it was on day 7 - I guess that could mean it's no good? I wanted to ask if anybody else has tried weighing eggs like this and if it sounds like a good idea? I can type up the formula if anybody is interested. Thanks.