This was not a scientific examination, but I believe that the "MN" code was used on Valjoux 72 movements spanning serial numbers from approximately 70xxx all the way up to 130xxx and even 170xxx.

Trying to assign dates to this range, my best guess would be circa 1966/67 to circa 1969/70.

I have only surveyed movements with Valjoux 72 movements, and not the other Valjoux movements (92, etc.).

I do not have a definitive explanation as to what this two-letter code indicated, but when we discussed this some years ago the suggestion was that the "MN" was used to indicate that a particular Valjoux 72 movement was made for Heuer.

Jeff

+++++++++++++++++++++++++++++++++++++++

: Hello Jeff

: Many thanks for your input.
: All the 2446 Autavia 1st execution watches that I have seen have
: numbered bridges but no "NM" markings, also not the
: 2nd execution watches with no numbers engraved on the bridge. On
: the other hand, on all the 3rd execution 2446s that I have seen
: the plates did have the "MN" engraving. That would
: date the switch to "MN" to about 1963/64.

: Thank you and best regards from Old Europe

: Richard