We were fortunate enough to wrangle a trip to Yucatan last year and visit the Mayan ruins at Chichen Itza. Inspired by Laura Gilpin's book Temples in Yucatan illustrated with her photos taken in the late 30's and early 40's, I took along my vintage Ikonta A 6x4.5 and dipped into my stash of Verichrome Pan. The Ikonta A 520 came out in 1933 and was replaced after the war by the 521. Mine has a 7cm f/3.5 Tessar (uncoated, of course) in a Compur Rapid shutter and has the 2 red windows with sliding cover for use with the 6x9 numbers on the backing paper. The number is first placed in one window and then the other to split the 6x9 spacing. Focusing is by guesstimation and the distances are in feet. A perfect pocket size and a joy to use. The later 521 is a little bulkier as it adds double exposure prevention, but it has coated lenses and a single red window for the 6x4.5 numbers.