I decided to create a separate entry rather than respond to the first entry in comments because some people don’t read those. If that describes you, half the valuable content on this site is in comments.
Louise asks:
I have been measuring each seam – carefully! – notch to notch, with a tape measure on its side. Why do you recommend walking the seams rather than measuring? What have I been missing out on by doing it this way?
When we say to “walk a pattern” we mean to check it. It doesn’t exactly mean walking pattern piece seam lines together but is a combination of various methods. In fact, I don’t walk patterns in CAD at all, I measure the lines and compare the lengths. There is no reason you can’t measure seam lines if you’re checking manually. One caveat; tape measures aren’t the best tool for this. I recommend a 2×18 B-95 ruler instead. Tapes can stretch so calibrating them is required. There is also a section of this video where I show how to walk with a ruler so I’ll have to dig that out too.