Numbers in this column are Teledyne-Post model numbers. They replaced the old Frederick Post model numbers about 1972.
Teledyne bought the Frederick Post Company about 1970 whereupon Post identifed itself as "The Frederick Post Company, A Teledyne Company." Shortly thereafter the company became "Teledyne-Post."
In 1972 Teledyne-Post switched to the "44" stock numbering system--the Versalog 1460 became "Versalog 44CA-600," for example. The last digit indicated minor variations in packaging: 44CA-60J was a Versalog rule with leather case and manual; 44CA-60H was a Versalog rule with molded plastic case and manual. Stock on hand with the old numbering system (e.g., "1447") was sold under the new numbering system. For example, some original boxes from this period were marked "Model 44BA-470" while their contents were marked "Model 1447."
Also in 1972 Teledyne Post expanded its line of slide rules to include
five all-plastic Hemmi slide rules. The first lot of these new rules carried
old model numbers (1410, 1420, etc) but the new numbering system
was in effect by the time they were ready for sale so they were sold as
models 44BB-100, 44BB-200, etc. The second lot of these rules bore
the new numbers. I'm not sure there was a third lot of these rules;
electronic calculators had destroyed the slide rule business by then.
That's why quite a lot of Post plastic slide rules with old model numbers
are in excellent condition today; their owners replaced them with electronic
calculators while the rules were still relatively new.