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More and more watches were using screw on backs and less were using the snap on type more typical of the early model ranges.
Case design was also developing and other case types were emerging.
The late 1950s also saw the introduction of serial numbers, which are very useful to us of course, because we can determine the date of production. Before covering the three basic designs, a word about the very early models.
Little information is stamped on the back – typically it may relate only to the case back material: I’ll provide more information on the early case backs in a ‘Featured Watch’ post on the Type F.
This page attempts to show the basic types and how to interpret the information that case backs give – often crucial to determining the authenticity of the watch. After the very early models using the ‘F’ type movement, Citizen began to develop a wider model range and towards the end of the 1940s and particularly in the 1950s a number of models were in production.Here is an example of a fully marked ‘transitional’ screw on back: Notes: 1) The back now has a circular outer ‘track’, with markings stamped around it and other information in the centre 2) The Model Number, or designation, is in the same style as the early format, usually a mix of letter and numbers Here are some permutations – the Autodater 7 appears to be etched rather than stamped, and (unusually) has no serial number, whilst on the Crystal 7 the model symbol fills the centre: These original illustrations are from a 1960s technical manual – the first shows the case type as ‘GN’ with different layouts: And here are the same with ‘OR’ designations – the same type of cases, so ‘OR’ means the same as ‘GN’ as far as I know but is less commonly seen: Note also that two case backs (see the two on the right in the above image) are marked with an encircled ‘x’.This means these cases are one piece that have to be opened through the glass, as on this Seven: Later Case Backs: The end of the 1960s saw the introduction of case numbers, distinct from the earlier combined model designation.Model names are not often seen on the back, but some now indicate the movement to be found inside – this is very helpful of course!Here’s a typical example of a fully marked back: Notes: 1) I have not been able to determine the system, if any, for model numbers – they generally do not help to identify the movement used.