It's a Deitzgen ESR-1. As your page says, it's an OEM version of the Casio fx-1. Casio sold the machines to Deitzgen, who just put their own modem/name/seria number tags on them, and was responsible for marketing and maintaining the within their marketplace. Sperry-Remington also OEM'd the Casio fx-1, and sold it under their brand name as the 1259S. Quite an interestng machine. It is essentially a basic four function calculator with square root, that added ROM-based "programs" using the besic functions of the machine to carry out the scientific functions. Some of the functions are very slow as a resylt. You can learn more by reading My exhibit on the Casio fx-1 at http://oldcalculatormuseum.com/casiofx1.html Rick Bensene The Old Calculator Museum http://oldcalculatormuseum.com