WatchProSite|Market|Digest

Rolex

Mike - Moderator from Rolexforums summed it up very well.

 

These are his words verbatim dates 0ct 16 2011
Early 5513s & 5512s can both be found with cal. 1530 movements. However, with the introduction of a free sprung balance with micro stella adjusters on the balance wheel & a Breguet overcoiled hairspring on the cal. 1560 ca. 1959-60 (and improved with the cal. 1570, ca. 1965) and the relative ease of achieving SCOC specs due to these improvements, these movements became Rolex's choice for their Chronometer-grade watches. The cal. 1520 was developed as a cheaper alternative for non-Chronometer watches only--Air-King, 5513 Sub, etc.--ca. 1965, as it uses a flat hairspring and a normal 'stick' regulator.
As an aside, there is a school of that holds that the very earliest 5512s (those manufactured prior to the ca. 1961-2 intro of the 5513) were not all submitted for chronometer testing, and this is why a majority of the earliest 5512 dials bear no OCC or SCOC markings and also why one can find cal. 1530 movements in both pre-cal. 1560 5512s and the early 5513s. In fact, throughout the years of its use, the cal. 1530 is only very infrequently found in SCOC watches and much more often in Precision or Super-Precision models. But while this is an interesting theory it remains only that for now.
Source: rolexforums
I hope Mike does not mind sharing.

  login to reply
💰1853 Marketplace Listings for Rolex