Once the four corners of the canton are assembled, they need to be stitched to the horizontal and vertical bars. This is a straightforward task, but worth double checking. I pinned and matched the pieces to be sure that the horizontals would be the same length as the blue and white rectangles, and then checked the two sides against each other. The pieces aren't always precisely even: the loose weave of the wool, the pull of the stitches, and the generous seam allowance can distort the pieces a bit as I work.
Once the two sides were assembled, I needed to check again: did they match each other? Did they match the vertical red piece? And would they match the top half of the field?
Reader, they did not.
The two sides matched each other, but that was the best they were willing to do.
This was not a great moment in flag-making history.
What to do? Fortunately the answer is both period-correct and simple: Piece the vertical bar! As for the field, that was another matter.