Swiss digital perpetual calendar with moon phases Circa 1937

Gold astronomical lever watch by Patek Philippe
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A very fine, extremely rare and thin Swiss 18 carat gold open faced keyless lever digital perpetual calendar dress watch with moon phases, circa 1937. Sold on December 27th, 1944. The rhodium plated with Geneva Striping decoration, 18 jewels, a straight line lever escapement, cut bimetallic compensation balance adjusted to heat, cold, isochronism and 5 positions, blued steel Breguet balance spring and an index regulator. Eccentric two-tone gold dial with applied gold Roman quarter hour numerals and gold baton indexes on a polished chapter ring, outer minute divisions, four apertures for days of the week, date, months of the year and phases of the moon, subsidiary seconds, original gold feuille hands. A polished case. Dial and movement signed, case and movement numbered. Accompanied by a fitted box and an Extract from the Archives.
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Diameter: 45 mm
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Signed: Patek, Philippe & Cie Genève
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This watch is the much rarer precursor of the linear digital calendar or so-called American (perpetual) calendar that was adopted by Patek Philippe in the late 1940s.
The American calendar indication is arranged in a single linear aperture.
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The linear digital calendar or so-called American (perpetual) calendar is a calendar in which the date is displayed in a single linear aperture, allowing for a legible dial to be read at a glance. This type of display was invented in the early Art Deco period and is most often found in watches destined for the Anglo-American market. This kind of calendar became popular once again after the Second World War.