A few have asked me lately on which block do you square? Good question; I had it once too. A tromp as writ pattern when woven correctly should be at a 45 degree angle starting at the right hand corner block. This is to insure that circles are round rather than looking like flat tires or Easter eggs. (-: Blocks run sequentially, sharing a common thread. If the first "block" woven is A, then the next would be B or D and share a common thread with that first right hand corner block. There are several things that determine a pattern being square. These include sett, beat, yarns, finishing and individual weaver; I'm sure I've left out a few. A pattern that is not square by tromp as writ can be squared by subtracting pattern picks in *some* places. I say *some* because care needs to be taken in order not to lose the integrity of the pattern. Also, turning blocks should always have an even number of pattern picks. I call this Barbara Miller's Rule #1; thank you, Barbara. If you're in question as to what the "rule" refers to, see Tromp as Writ.
Some coverlet weavers include an extra yard for weaving a sample, then wet-finishing to determine the number of picks to subtract. Of course, this means cutting off, retying, etc., but, it does work. Looking at the corner right hand block, you would determine how many pattern picks need to be subtracted from that corner block to make that corner block square. Then, look at the next block that runs at an approximate 45 degree angle up and to the left and do the same thing, remarking your original tromp as writ treadling.
Here's my way and it works most of the time for me as I have a, generally, even beat. (Everyone's is different.) I include some extra for sampling - yes, the "s" word. *However,* I weave enough of the border and the pattern by my tromp as writ treadling to determine whether it's going to be square. Then, *without tension* I place the center of a protractor over that first right hand corner block and see what degree of angle I have going. I figure in about 10% shrinkage and if the angle is 49.5 degrees it is going to be close when it is wet-finished. If it's more, which it usually is, I set the protractor at 49.5 degrees and count the number of pattern picks over the 49.5 degree mark and subtract within individual blocks of the treadling order. No, I don't like the "s" word either; that's the reason I use this method.
Here is an exercise I did using Fiberworks PCW to give an example of squaring. The tromp as writ pattern now has a 49 pick repeat as opposed to a 61 pick repeat. You can probably tell that I removed picks from the table or last motif. The square appears to be flat in the drawdown because the fiber program is a perfect world and does not take the necessity of squaring into account. You will note that I was very careful to leave the turning block an even number and subtracted from the blocks on either side of the center. I also did not subtract from transitional blocks, those having only 2 threads in the block.