Rare Swiss aluminium centre seconds siderograph Circa 1943

Aluminium siderograph in gimballed mahogany deck box by Longines
–
A very rare and beautiful, manual winding, Swiss aluminium marine chronograph siderograph with centre seconds, seconds recorder, split seconds, 36 hour power reserve indication and stop feature in a gimballed mahogany deck box, circa 1943.
Rhodium plated movement, Geneva striping decoration, 17 jewels, straight line lever escapement with beryllium pallet fork, monometallic balance, self compensating blued steel Breguet balance spring with a micrometric cam type regulator, chronograph work visible on the backplate. Two tone silver dial with Arabic numerals double graduated rotating bezel, outer revolving blue chronograph ring, tachy scale, and power reserve sector below the 12 o’clock. Deck box with brass bound corners, aluminium gimbal and external start stop for the chronograph. The inner: cylindrical, massive, back secured by five screws,  glazed back removable screw on weight to work with the gimbals. Dial, movement, and deck box signed.
–
Deck box: 15 cm x 15 cm x 10 cm
–
Diameter inner: 94 mm
–
Signed: Longines
–
Invented by Longines in 1938, the Siderograph measures Greenwich (0 longitudes) Sidereal or Civil Time in hour angles, minutes and minutes of arc and can be considered the final evolution of the marine chronometer. These timepieces allow the user to navigate at night and during the daylight hours more accurately than the Weems and Lindberg systems for nocturnal navigation that were heavily reliant on radio time signals. The Siderographs were based on the chronometer calibre 2129, which was Longines’ most accurate movement. The calibre was modified with the addition of the split seconds mechanisms and anti magnetic beryllium pallet fork. The movement was then cased in a heat toughened aluminium case. This is a non magnetic, light, nonferrous material suited for aeronautic and maritime applications. The present watch is one of a handful of examples known to exist in a gimballed deck box, indicating it was intended for use aboard a ship.
The siderograph was created to facilitate the calculations of sailors or airmen by giving Greenwich Mean Time directly in degrees. The dial is not divided into 24 hours but 360 degrees.