That can make it difficult to find

Dating post slide rules

The presence of two serial numbers on a given rule was to facilitate manufacturing allowing the mating of pieces of rules in final assembly. Serial numbers on the rules are discontinued.

This serial number sequence has not been studied at this date. The case is also hand-dated to Nov. In fact, this table seems to be virtually identical to my earliest Faber model. One can estimate dates of Hemmi slide rules from markings on the rules. It is obvious that the production rates did not change at these dates exactly.

We are sure that this wasSome have serial numbers

We are sure that this was in the early s while they were working through old series stock. Some have serial numbers and some do not.

The cursor is the later model metal-framed glass, which I believe came into play sometime shortly before the second world war. Indeed, apart from its diminutive size there is no real difference between this rule and its full-size sibling. There is at least one mistake in these cross reference numbers. The common rules were produced in regular batches but the specialty rules did not sell as well and a given batch of rules might stretch over several years. It sometimes takes inspection with a magnifier in raking light to find the code.