According to Eric Marcotte, this circular was in force from 1914 to 1936.
Keuffel & Esser 4088-3 10" Duplex This slide rule may be even older, but I can't be sure. The indicator is frameless glass with plastic edges held together with metal screws. K&E stopped selling model 4092-3 in 1938, when it was priced with a leather case at .75. The left end of the slide and the front of the base are marked with a serial number: 373480. The prefix was dropped in 1936, but the indicator was replaced with a new version of K&E's frameless indicator.This 4041 has the celluloid cursor blocks that replaced the metal ones in 1914-1915 model (above), and it doesn't have a serial number so it has to antedate the 1922 model below. We know this rule dates to 1922 because of an odd feature.Before 1922, K&E stamped the left ends of both the slide and stator with short 2-3 char codes that could be used to keep the parts together during manufacturing.