It soon became clear that the swatch with 4 mm needles was going to be too big, so I didn't complete the swatch. I knitted one with 3 mm needles. It was too dense and not quite big enough. I don't have 3.5 mm needles, but I had a look through my circular needles and found 3.75 mm. That swatch has the right width but measures 9 cm long where it should be 10 cm. Hmmm. I looked at the pattern carefully and decided I can add some extra rows of stocking stitch to make up the difference. I'm starting with the Right Front, because I think it'll be easier to match the the back to the fronts than vice versa. So far, so good, I've just got to remember to write down where I put the extra rows in, so that I can match it on the Left Front.