they are square, that's not being disputed. well not now anyway. it is sometimes difficult to remember that the "extra" 1/2 is on the side. I make mistakes with that and I've been quilting over 20 years. so we all can get confused. just saying....

This whole thread is over my head! If I were not confused at the beginning of it, I surely am now!

All of you have great minds to be able to explain this.

I am lost, too, but underneath it all, I think I get it, because I've never questioned it. I do believe, the explanation is simpler than we're making it and the bottom line is, as many have said, so it adds the seam allowance and makes it easier to square up.

Now go square up your blocks, LOL.

Thank you so much for posting this link. It was exactly what I needed to know.

http://www.quiltuniversity.com/squaring_up.htm

This short video shows cutting actual fabric, and is easier to understand than computer generated graphs. Those graphs are so helpful most of the time, but on this one, we want to see the uneven edges that need to be trimmed off.
Also, you don't really need special rulers. People that have them say they are worth the money, but it is possible to do this with any rotary ruler. The big ones would be very clumsy, but it is doable.

I was getting quite confused too. So I went to my only square ruler which I use a lot, 6 1/2". It has 1/4 inch allowed on all four sides. So that is what I am used to...no wonder I couldn't understand the 1/2 inch on one side and none on the opposite side...My ruler is by Marti Michell. Have had it a long time.
There, I feel better now! :-)

well don't worry about it. if this confused you it only means you've never been confused by a ruler. that's a good thing.