Aha! - It appears that the french sizes I discussed in the last blog are based on 'Rules of Composition'.
The Wikipedia explanations are in french here:
http://fr.wikipedia.org/wiki/Règles_de_composition_dans_la_peinture_occidentaleMike
News and views from Xaintrie, a sub-region in South-West France. It nestles largely in the extreme south of the Department of Corrèze, in the region of Nouvelle Aquitaine. Nouvelles et points de vue de Xaintrie, une sous-région du sud-ouest de la France. Il se niche en grande partie à l'extrême sud du département de la Corrèze, en région Nouvelle Aquitaine.
Also -look at this site:
http://alain.joly91.free.fr/paged_accueil_tailledestoiles.htm I've been trying to trace the historical basis for these French traditional shapes but haven't got very far. Does anyone have any info on this subject, I wonder? Mike