Hi Torsten,
Thank you so much for your help. I can adapt that to my needs.
It is surprising that the open circle and the filled ones of various sorts in Unicode have different bounding boxes. And that's a great tip for showing the bounding box. You would think these circle glyphs would often be used together. I wonder if that is a font issue. I am using Linux Biolinum 0. May be worth my experimenting with other font renditions.
I really appreciate this. I may well end up writing Postscript as I think I am going to need quarter filled circles and other non Unicode glyph objects later on, and I am fluent in Postscript, but using text spanners is great for now as I can show the results pretty well, and quickly.
Andrew