Paul Chamberlain, It's about Time, 1978, pp.463-7;
....M. Paul Ditisheim excelled in every form of watchmaking. He made the smallest watch in the world for the Sultan of Morocco, he designed and executed timepieces of great precision, and exhibited enviable talent as a regleur of his own pieces. He collaborated with Dr. Guillaume in the application of Invar and Elinvar, and produced by their own use and to his own invention of an 'affix', or very small bimetal compensation to the solid balance, a movement which made new records at most of the observatories of the world. A silver cased nineteen jewel, 'up and down' indicator watch, costing sixteen dollars at the factory, sent by me to the Bureau of Standards, took a First Grade Certificate'.