Reference:971: Difference between revisions

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Two distinct caliber generations appear in 971 cases, and they are visually identifiable from the movement plate shape:

* ~~'''~~Cal. 300 / Cal. 350 — rectangular plates, 1928–1935.~~'''~~ 7½ by 14½ lignes. 18,000 vph. Approximately 50-hour power reserve. 15 jewels at the Prima base; 18 jewels at Extra Prima and Ultra Prima with 6-position adjustment. Phillips Geneva V lot 212 documents a platinum 971 with Cal. 300 7½′′′ 18-jewel movement in case 6,013 dated 1935.

* Cal. 300 / Cal. 350 — rectangular plates, 1928–1935. 7½ by 14½ lignes. 18,000 vph. Approximately 50-hour power reserve. 15 jewels at the Prima base; 18 jewels at Extra Prima and Ultra Prima with 6-position adjustment. Phillips Geneva V lot 212 documents a platinum 971 with Cal. 300 7½′′′ 18-jewel movement in case 6,013 dated 1935.

* ~~'''~~Cal. 360 HW — tonneau plates, 1936–late 1930s.~~'''~~ The successor caliber for the late-period 971s and the 1936-onward Prince family broadly. Auction houses routinely lump both calibers as "Prince movement" without distinguishing the plate shape; the NAWCC discussion (Doug Sinclair, gmorse, Cary Hurt, March 2013) is the load-bearing source for the cal. 300 versus cal. 360 split. A 971 with rectangular movement plates is a 1928–1935 example; a 971 with tonneau plates is 1936-onward.

* Cal. 360 HW — tonneau plates, 1936–late 1930s. The successor caliber for the late-period 971s and the 1936-onward Prince family broadly. Auction houses routinely lump both calibers as "Prince movement" without distinguishing the plate shape; the NAWCC discussion (Doug Sinclair, gmorse, Cary Hurt, March 2013) is the load-bearing source for the cal. 300 versus cal. 360 split. A 971 with rectangular movement plates is a 1928–1935 example; a 971 with tonneau plates is 1936-onward.

Movement grading runs Prima → Extra Prima → Ultra Prima, corresponding to ascending jewel counts (15 → 18), adjustment positions, and chronometer testing rigour. The "Chronometer" or "Observatory" designation on the dial indicates Extra Prima or Ultra Prima grade. The Kew-Teddington observatory tradition runs through this period — Rolex submitted Prince movements to the National Physical Laboratory at Kew for independent rate certificates against the Swiss Bureaux Officiels Suisse de Contrôle. Antiquorum's May 2013 platinum 971 (case 6,077) noted only the fourth platinum 971 sold through that house at the time, suggesting that platinum-cased Princes were specifically reserved for the highest movement grades.

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 Two distinct caliber generations appear in 971 cases, and they are visually identifiable from the movement plate shape:
-* '''Cal. 300 / Cal. 350 — rectangular plates, 1928–1935.''' 7½ by 14½ lignes. 18,000 vph. Approximately 50-hour power reserve. 15 jewels at the Prima base; 18 jewels at Extra Prima and Ultra Prima with 6-position adjustment. Phillips Geneva V lot 212 documents a platinum 971 with Cal. 300 7½′′′ 18-jewel movement in case 6,013 dated 1935.
+* Cal. 300 / Cal. 350 — rectangular plates, 1928–1935. 7½ by 14½ lignes. 18,000 vph. Approximately 50-hour power reserve. 15 jewels at the Prima base; 18 jewels at Extra Prima and Ultra Prima with 6-position adjustment. Phillips Geneva V lot 212 documents a platinum 971 with Cal. 300 7½′′′ 18-jewel movement in case 6,013 dated 1935.
-* '''Cal. 360 HW — tonneau plates, 1936–late 1930s.''' The successor caliber for the late-period 971s and the 1936-onward Prince family broadly. Auction houses routinely lump both calibers as "Prince movement" without distinguishing the plate shape; the NAWCC discussion (Doug Sinclair, gmorse, Cary Hurt, March 2013) is the load-bearing source for the cal. 300 versus cal. 360 split. A 971 with rectangular movement plates is a 1928–1935 example; a 971 with tonneau plates is 1936-onward.
+* Cal. 360 HW — tonneau plates, 1936–late 1930s. The successor caliber for the late-period 971s and the 1936-onward Prince family broadly. Auction houses routinely lump both calibers as "Prince movement" without distinguishing the plate shape; the NAWCC discussion (Doug Sinclair, gmorse, Cary Hurt, March 2013) is the load-bearing source for the cal. 300 versus cal. 360 split. A 971 with rectangular movement plates is a 1928–1935 example; a 971 with tonneau plates is 1936-onward.
 Movement grading runs Prima → Extra Prima → Ultra Prima, corresponding to ascending jewel counts (15 → 18), adjustment positions, and chronometer testing rigour. The "Chronometer" or "Observatory" designation on the dial indicates Extra Prima or Ultra Prima grade. The Kew-Teddington observatory tradition runs through this period — Rolex submitted Prince movements to the National Physical Laboratory at Kew for independent rate certificates against the Swiss Bureaux Officiels Suisse de Contrôle. Antiquorum's May 2013 platinum 971 (case 6,077) noted only the fourth platinum 971 sold through that house at the time, suggesting that platinum-cased Princes were specifically reserved for the highest movement grades.