Reference:Movements: Difference between revisions

<div class="rp-era"><div class="rp-era-name">Milgauss</div><div class="rp-chips">[[#cal-1580|1580]] [[#cal-3131|3131]]</div></div>

The early Oyster chronograph references use Valjoux ébauches, with Rolex caliber designations that should be kept distinct from the maker’s base number. Available auction records support a limited Cal. 13 / Valjoux 23-family entry; they do not establish that every early Rolex chronograph used the same execution.

Jarman dates Cal. 360 to 1937. The expansion of the HW designation remains unconfirmed; it should be retained as a designation rather than expanded to Hans Wilsdorf. The differing shape and jewel descriptions need comparison with the movement in the individual watch.

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This Aegler-supplied 10½-ligne hand-wound family uses the 700/710 architecture. It has a straight-line lever escapement, monometallic Superbalance adjusted to six positions, self-compensating Breguet balance spring, and swan-neck micrometer regulator, with no documented shock protection. Antiquorum names Cal. 700 in its catalogue for ref. [[Reference:3358|3358]], case 51,419; this is a lot-specific attribution. The movement powers the original Air-King 4925 and its Air-Lion, Air-Tiger, and Air-Giant siblings, including the sub-seconds 4365, mid-size 4444, and 4647 Hunter Precision. Its architecture links the pre-war Prince and Bubbleback movements with the post-war automatic Cal. 1030. Cal. 700 and 710 are hand-wound movements; Cal. 720 belongs to the automatic branch. White’s *The Vintage Rolex Field Manual* maps [[Reference:5031|ref. 5031]] to Cal. 710 in a reference table, but auction catalogues describe 5031 examples as automatic date watches. Christie’s [https://www.christies.com/en/lot/lot-204100 listing] records movement number 37519 but no caliber; Antiquorum’s [https://catalog.antiquorum.swiss/en/lots/rolex-lot-120-203 1995], [https://catalog.antiquorum.swiss/en/lots/rolex-lot-53-191 1999] and [https://catalog.antiquorum.swiss/en/lots/rolex-lot-222-285 2009] entries do not name a caliber and report differing sizes and jewel counts. Sotheby’s 2020 and 2022 entries say only “automatic.” The available records do not resolve the conflict, so the 5031 is not assigned to Cal. 710, A.295, 740, or 745 here.

Christie's places the ref. 6494 changeover between a circa-1956 example with Cal. 1210 and a circa-1958 example with 1215. Other documented fitments include the Speedking 6430, early 6694 production, and refs. 9996/9919. Refs. 6094 and 6294 used Cal. 740 and 790 respectively, rather than 1215.

Cal. 1030 is a bidirectionally wound automatic used in 1950s Oyster references. Its 5.85mm profile ended the domed Bubbleback caseback, while the cutaway "butterfly" rotor stamped ROLEX PERPETUAL PATENTED is the usual visual identifier. Finishing includes perlage on the rhodium-plated main plate, brushed bridges, polished screw heads and red anodized-aluminium reversing wheels. A conventional index regulates the movement; the visible regulator arm distinguishes it from the later free-sprung 1560 and 1570. Documented fitments include ref. 6098 from 1952, Submariners 6536, 6536-1 and 6538, Explorer 6610 and Air-King 6552. The same movement appeared in chronometer and non-chronometer watches.

Cal. 1530 ran from 1957 to 1965. Its 17-, 25- and 26-jewel versions are concurrent market variants, not a chronological progression. Seventeen-jewel movements appear in a 1958-era ref. 5508, a 5500 and a 1011 Eaton, and Rolex’s Technical and Service Information, third edition, discusses the 1520 and 1530 families in its servicing instructions.

The 1530 first entered the Submariner in ref. 5508, followed by 5510; neither was chronometer-rated at launch. It replaced the 10-series in non-chronometer watches, including Precision models, the Air-King, ref. 5504 "Super-Precision" Explorer and the Canadian Explorer-Date with Cal. 1535. Certified models such as the 6542 GMT, 6610 Explorer, Datejust and Day-Date retained 10xx calibers for longer. Strongly documented fitments include refs. 5508, 5510, 5512, 5513, 5500 and 5504. Single-lot support exists for 5501, 5502, 5506, 5516 and 5590/1011 Eaton. Bonhams listings for refs. 1002 and 1003 are internally inconsistent and remain unconfirmed. Bonhams lot 84 lists caliber 1530 in ref. 1003 case 573,835 and notes a chronometer certificate dated 22 December 1960. The catalogue is the evidence for this individual attribution; it does not resolve why common reference tables omit the 1530 for 1003.

Jewel counts of 17, 25 and 26 reflect parallel market executions. Rolex balance-assembly numbers confirm a flat hairspring for the 1520 and 1525, against a Breguet spring on the 1530 and Microstella on the 1560. The 1525 remains index-regulated.

Cal. 1560 arrived in 1959 as the chronometer-grade 15xx movement, with a free-sprung balance adjusted to temperature and five positions. Auction catalogues give both 25 and 26 jewels without establishing a pattern. Antiquorum usually describes a Breguet overcoil; its flat-hairspring description for one ref. 1502/1503 is an outlier.

Cal. 1570 is the 19,800-vph revision of the 1560, introduced in 1965. One Artcurial ref. 1005 lot is catalogued with Cal. 1550, despite a chronometer-dial description; other 1005 catalogues list 1560 or 1570. This single lot does not establish a 1005 movement variant or resolve whether the movement is original. It retains the free-sprung Breguet overcoil and Microstella regulation, with adjustment to temperature and five positions. Family-wide bridge engraving causes date movements such as the 1575 in a ref. 1665 to appear marked 1570; the engraving alone does not identify the exact caliber.

Rolex introduced the documented Milgauss calibers about fifty years apart. Rolex adapted its contemporary sport movements for the Milgauss: Cal. 1580 derives from the 1530 platform, and Cal. 3131 from Cal. 3130.