One aspect that I can't seem to get the hang of is final proofing.  I have overproofed, underproofed, and when I get it right it feels as much chance as anything else.   Yesterday I started off making Hamelman's Pain Au Levain with 5% rye flour.   I have made it once before, and felt that I overproofed it just a bit.   Today, as I was mixing the dough I realized I didn't have anywhere enought bread flour.   I didn't want to substitute AP, so instead I put in 1/2 bread flour, 1/4 rye, and 1/4 spelt.   So already I had deviated significantly from the formula so I had no idea if the techniques would still work.   I let the bulk ferment go for the 2.5 hours he specifies.  He specifies 2-2.5 hours for the final ferment.   He also says the following: "As you feel the outside of the loaf with your finger, try to sense what is going on inside ... The dough should feel light, somewhat loose, somewhat weak..."   I really have no idea what he is talking about and wish I did.   But anyhow, today, I prodded the dough with a wet finger after 30 minutes, and it left an indentation.   So even though the time was so short and even though I had no idea if that meant the dough was light, loose, or somewhat weak, I decided to pop it in the oven.   It got a lot of oven spring, but split along the bottom seam, and the crumb is pretty tight, so did I bake too soon?  How do you know when it's ready to go in?  Thanks!  Varda