When you warp on a board or a mill, you're supposed to push each yarn layer snugly against the previous layer. I've done OK on the top peg here, but there are at least two warps markedly out of place on the bottom peg. But that's not what I wanted to focus on.
As seen in this photo, yarns start from the top, create a cross, go around all pegs, turns around at the bottom peg, and come back up. So they go around all pegs twice but only once around the top and the bottom pegs, so the top and the bottom pegs have half as many yarn layers. With the top peg, being right next to a cross, there is not as much packing, but on my bottom peg, seen here at the top, this is quite noticeable.
This means that as I put more warp yarns and layer them on the board/pegs, the warp yarns become slightly but increasingly longer. In addition to all other self-inflicted irregular tension problems, I have noticed time after time the left side of my narrower warps ever so slighting being looser. I used to put it down to my looms not being square, or something to do with the bake mechanism being on the right side of the looms, but could this be it? If so, adding the extra pegs at the bottom of my board should remedy this somewhat.
And again, if you think about it, how obvious is that!
PS. Please ignore the Manila folder in the above photo; I was trying to photograph the trapezoid the warps were creating, but couldn't manage.