Hi Fernando, I don't have Waugh, so cannot comment on your main query, but you also ask:
PS -- Both Abert Waugh and Rene R. J. Rohr say that in a vertical dial the 12 o'clock line is always vertical. Nevertheless, I've noticed this is not the case for a vertical direct west (or east) dial. Have I found a hint here? [Chris Lusby Taylor] I think you are wrong. A vertical direct east or west dial does not have a 12 o'clock line! At 12 o'clock the sun is in the plane of the dial, so the shadow of the gnomon does not fall on the dial. A very very nearly direct east or west dial does, in principle, have a 12 o'clock line, and it is vertical, passing through the point where the gnomon touches the dial. Unfortunately the gnomon is almost in the plane of the dial, so it protrudes only a very small amount and it is not very practical. This is why direct east and west declining dials are always made with the gnomon held away from the dial. Hope this helps Regards Chris Lusby Taylor
