If my type design’s stems aren’t parallel at all (for example suppose they are shaped like tall trapezoids), what would be the best value to put into the Vertical Stems setting?
Depends. What for? Hinting? I’d have to see the design to tell you if hinting makes any sense in the first place.
Yes, hinting, and playing with RMX tools. I’ve sent a pic to you.
I would measure the middle of the stems
Make sure you have extremum points at the thinnest part, then you can take the x distance between the extremum points. I believe this is also what Georg means.
But you don‘t have to be overly precise with these values, you know. Approximate values will do.
I mant use an average of the thickest and thinnest value. This would serve best for RMX. Hinting does not work well with nonvertical stems.