elnan

In this picture, the sewer is stitching through at least 2 layers of fabric, using a speciality foot. I'm curious about the straight line of stitches just above the zigzag, or is that a folded edge shadow? There was a time when sewing patterns called for different edge finishes to seams, such as pinking, binding, french seams, or zigzag. A zigzag edge was so much easier. One thing you soon learned was that zigzag edges did not work well on a single layer of fabric, the stitches curling the edge. Thick knits worked fine with a single layer, but you had to work out the tension to stitch length on a practice piece. Any thinner fabric was a puckered mess. I've never seen the instructions for folding over the edge as shown in this picture, what machine would that manual have gone with?, but in those days I probably wouldn't have bothered reading a manual, thinking all machines worked the same.
By the way, I'm probably much older than your vintage machine that would make a zigzag stitch.