Oh, puleeeze! I'm wrong just as much as I am right. Barred Rocks are much easier than most, one of my main breeds I keep. It's just an art and after a few years of observation and owning boys and girls of several breeds, you just learn to see the signs. I've learned to look quite often at the thickness of the legs more than the combs on many breeds, although that doesn't work on some as much as others. For instance, the Ameraucanas don't have thick legs in either sex and the Orpingtons have tree-trunk legs in both.
Jdypat, that word "vent" sure is an odd one for the place where both poop and eggs come out, isn't it? Vent, ventilation, air, nose, I see where your mind went. Perfectly logical. Heck, they even call the nostrils on birds "nares".