So, since we have already had a buttonhole variation I am calling this one Buttonhole Variation 2. It is worked on a line which curves back and forth across the seamline. The "legs" of the buttonhole are always on the outside of the curves in this variation. I've included a couple photos below just by way of further explanation.
The first thing I did was to mark my line for stitching. I used a votive candle for my curve template.