Thank you all for the links, tips, and photos. Such lovely and inspiring examples. I think I will look into the ruler. Initially I didn't want to invest in it, as I don't think scallops will be a frequently used treatment on my projects, but it looks like it makes the whole process so easy and quick. We're working against a deadline here, so that quick part, with minimal fussing and trial and error, is key.
Again, thanks everyone for your helpful input.
RST