Swiss 18 Carat gold keyless pocket lever chronometer Circa 1915

Gold open faced lever pocket watch
–
A very fine and rare Swiss, 18 Carat gold keyless pocket lever chronometer, circa 1915.
With extra quality movement made for Observatory Trial, power reserve and Guillaume balance. Accompanied by an Extract from the Archives. A polished case hinged back with engraved monogram, demi concealed hinge. Hinged gold cuvette with engraved presentation inscription. White enamel dial, black Paris numerals, outer minute track and red Arabic five minute numerals, subsidiary seconds with red numerals, power reserve sector below 12 o’clock with red numerals. Blued steel fancy hands.
–
Movement with Geneva striping decoration, wolf’s tooth winding geared to an extra wheel operating the power reserve indicator, special mainspring ratchet wheel click preventing overwinding, 21 jewels, counterpoised straight line lever escapement, Guillaume balance with gold and platinum screws, eight adjustments, blued steel Breguet balance spring with a terminal curve, swan neck micrometer regulator, diamond end stone.
Dial, case, cuvette, and movement signed, movement numbered twice.
–
Diameter: 50 mm
–
Signed: Patek, Philippe & Cie.  Genève
–
The movement of this watch has the unusual winding click only found on a very small number of Patek Philippe watches made for the Observatory trial. When destined for Observatory Timing Contests, the movements of Patek Philippe watches, like those of other makers, were double engraved with the movement serial numbers. The inscription “Extra” on the bridge of the movement refers to the high finishing of all the parts of the movement.