These are good quality movements, not COSC, which would be 5 positions, but very few were at the time. During the late 50's and early 60's, watch testing for chronometer status was carried out by the Bureau Officiels de contrôle de la marche des montres and the mean daily rate limit was -1/+10, compared with today's -4/+6. (This must be achieved with a narrow delta in five positions) COSC was established in 1973.
In 1957, a watch like this only lacked the certificate to be called a Chronometer. The definition at the time was:
“a chronometer [was] a precision watch, which [was] regulated in several positions and at different temperatures and which had received a certificate [from the (“B.O.)]."
These were definitely not run of the mill watches, and in-house, USA made, to boot.
1957 Bulova 23 'A'.
Hi Reverend Bob
That is very illuminating info. This particular watch is perhaps as accurate as any I own. not sure how many of these movements I have, but a few. the 6 adjustments has always appealed to me. This one is more dead-on than (dare I utter it) my Omegas. My first love is American movements, but I'm not over the top with that