Mainly because there worthless and populated with fake profiles.
1932-1941 - Hemmi-manufactured rules have no date code and are marked "Made in Japan" 1942-1946 - WWII.Dates that a design was registered or patented only suggests an approximate year a model may have been first produced, as the model may have been distributed a year or more before issuance (patent pending). There were three rollovers occurring in 1943-1944, 1954, and 1962.The patent may only refer to a certain combination of scales used over a thirty year time on different models. 1911 James Dieterich, who has worked his way up to blueprint foreman at B. Makepeace Co., goes west and lands a job as a salesman with the K&E branch in San Francisco. In general the production rate was about 70,000 rules per year until the 1950s. The 1960s had a production rate of about 100,000 per year for several years and tapering off in the 1970s ending at about 700000.We are sure that this was in the early 1960s while they were working through old 4000 series stock.Post sold a wide variety of slide rules, both under its own name and under the names of various manufacturers.