I have found the ruler and it is called a Tailor Perfect Half-Square and Quarter Square Triangles Ruler. Which is great except that I had no instructions with it, talking of which I shall go and Google it to see if some are online.
I have spoken to the quilt shop who send me the bom and the lady there says that she is making everything in HSTs using this ruler and the square on square, sew and cut method for HSTs and not using any triangle to triangle sewing.
Well, I have worked it out and this is all very well, except that some of the HST blocks become very small with this method, especially in block 3 - not small for people who make miniature quilts of course, but I expect they use foundation anyway, and I can never get the hang of that! So triangulations are out. Good luck, Cherylynne and Chickadee, please do let me know how you get on and what your lady says Cherylynne - are you doing the whole thing on foundation?