It can be inferred from used expression "photographic plates" that were used much more in 1922, when Crawford and his successors carried out their first investigations, than in the sixties, when Deuel gathered materials for his publication.
Inaweza kutumika alichokuwa anamaanisha kutoka kujieleza "sahani za picha" kwamba walikuwa kutumika zaidi mwaka 1922, wakati Crawford na warithi wake uliofanywa uchunguzi wao wa kwanza, kuliko katika miaka ya sitini, wakati Deueli wamekusanyika vifaa kwa ajili ya uchapishaji wake.