The comparative method of punch impressions study initiated by the author for the problems of attribution is demonstrated. Details are photographed in life-size with a cm scale juxtaposed. A comparative chart of the punch repertory and a dozen photographs of details show that the current attribution to the Florentine Nardo di Cione is untenable, and that the altarpiece issued from a Pisan workshop close to Turino Vanni. The individual shops owned sets of specific motif' punches, the use of which appears to have been restricted to the members of the studio. M.S.F. -- AATA