CR - the reason for my post above was to (hopefully) demonstrate that the rule of seven is a natural consequence of using a seven note scale.

My post reads exactly as I intended: in Ab there are four flats and three natural notes. Move everything up one half-tone and you end up with four naturals and three sharps.

My hope was to add to Mary's understanding of the 'trick'.

A fiddler can play any key using only stopped strings; the comma doesn't enter into it, nor the 'tempering'. Many folk styles (if not most) use open strings where available both for melody notes and/or drones. That's when B becomes problematical.

Stu