Notes: "Keuffel & Esser stopped making slide rules in 1975, which is probably about the time that this calculator, the Model 68 0800, appeared. It is not listed in the 1972 catalog. The 68 0800, a wall-socket powered 4-function calculator, would have had a very short life, what with the rapid advancements in pocket calculators at the time. To put it in perspective, in 1975 the HP-35 had been around for three years and was discontinued, replaced by the more capable HP-45. This 68 0800 is serial No. 0436 A. "