The latest issue of Popular Woodworking has an article by Jim Tolpin on using a sector, a hinged tool for scaling and proportions. It highlights enough cool tricks that I began thinking of making a version for my own use. There is a picture of an old sector attached to the article. That version has several scales marked on the blades including some marked on an angle. This is hard to imagine without a picture.
Here is my question. Any ideas about the calculation functions of those "angled" scales?" Scales that run parallel with the blades are obviously useful for proportions but I can't think far enough to see the use of the angled scales.