Sewing, for the most part, is an exact art. It matters whether or not seams match up. It matters what direction napped fabrics are cut and it matters whether or not prints match. In quilting, cutting exact sized blocks is very important to the finished product. This applies to standard pieced blocks as well as to embroidered quilt-as-you-go blocks. I have found the most accurate method of squaring up embroidered blocks is to use the quilter’s 150×150 or the 200×200 hoop, both of which come with a plastic template that fits inside the hoop.
I use a heat erasable pen to mark both the X and Y axis as well as the diagonals.
(I use the heat erasable pens because they don’t fade over time. No matter how long it takes me to complete my project, the marks remain until I use the heat of the iron to erase them.) Once the material has been marked and the design embroidered, the marks remain. By marking the X and Y axis as well as the diagonals, I can then line up my squaring ruler, no matter what kind or size I use, for the most accurate cut to obtain a perfectly square block.
Once the block is squared, I do not erase the marks, but now use them as hash marks to perfectly align the blocks into the larger configuration. (On the left block the marks are in red and on the right block, they are in black).
In this way I can try out different layouts and be assured that, no matter what layout I decide to use, my blocks will be perfectly aligned when stitched.
This technique also ensures that embroidered quilting backgrounds that you may create in embroidery edit from your built-in quilting stitches on the sewing side of your machine (if your machine has that capability) will also match to mimic continuous quilting.