found: Nichols, A.S. Manual for the pointer ... 1944.
found: Hundert Jahre Weltsensationen in Pressefotos, 1980:p. 1 (Bildagentur Keystone) p. 348, etc. (Keystone View Company establ. 1891 in Meadville/Pa.; Keystone Agentur)
found: Lanzmann, J. Paris des année 30, c1987:t.p. (Keystone) jkt. (Agence Keystone)
found: Tel. call to Joe Deal, U. of Calif. Art Gallery, Riverside, 8/1/78 (x-ref.)(Keystone Company founded latter part of 19th century, ceased to exist 1930; produced stereographic plates)
found: Yellowstone stereoview page (website), viewed May 2, 2013(Keystone View Company; Meadville, PA, New York, Toronto, London, Sydney; founded 1892 by B. L. Singley in Meadville, PA; by the 1920s the Keystone Company was the sole surviving major producer of conventional card-mounted views in the world; the company survived into the 1970s; remaining images/prints went to the California Museum of Photography, Riverside, CA)