Futurematic

The Futurematic is a self-winding wrist watch without a crown. It was manufactured between 1951 and 1959 by the Swiss watch manufacturer Jaeger-LeCoultre. The Futurematic was the world's first watch without a crown for winding the mainspring, having a flat crown on the back that was used solely for setting the time.
Watch face.
The Futurematic was produced with two different watch dials. Both dials have a central time indicator for hours and minutes. The earlier dial has a small second indication and a power reserve indicator and was used in model "E501". The later dial version called "Futurematic Porthole" had two portholes and was used in model "E502". Below these portholes are rotating discs, one as a power reserve indicator with a colour change of red or blue (two variants, with the color indicating "high reserve") to white (for "low reserve"), the other porthole had a disc with an arrow to indicate the seconds. The watch calibres K497, K497/1, or KP827 were used for the model E501, whereas the E502 contained K817, K817/1, or KP837.
Movement features.
All calibres contain a seconds hacking mechanism, which stops the watch when the crown is slid towards the centre, as well as a centrally suspended rotor for winding the mainspring and thus increasing the power reserve. The rotor swings bidirectionally through an angle of about 190°. All Futurematic calibres contain an antimagnetic and an enlarged and heavier (by about 20%) balance wheel, as well as a regulator for the balance spring with micrometre scaling and a unique wire hook mechanism to prevent overwinding of the mainspring. A complete unwinding of the mainspring was mechanically inhibited to allow the watch to start running shortly after putting it on the wrist. The last calibres of both models have "Parachoc" shock protection and therefore contain a "P" in the name, P827 and KP837, whereas the first calibres possess "KIF" shock protection. The comparably elaborate construction of the Futurematic was the base of the advertisement slogan at the time - "the most accurate self-winding watch in the world".
Versions.
Due to the Smoot–Hawley Tariff Act the Futurematics for the U.S. market have a "LeCoultre" logo instead of "Jaeger-LeCoultre" printed on the dial and engraved on the calibre and the inside of the case back. As an exception to this rule, all case backs of U.S. and European Futurematic models are internally engraved with "LeCoultre", whereas the other markings differ. The cases of the U.S. models and the dials which were produced in the U.S., encase a Swiss-made watch calibre engraved "LeCoultre". The U.S. models were distributed by the company Vacheron-Constantin-LeCoultre, a subsidiary of Longines-Wittnauer. Therefore, there are differences in the case forms and the dials between the U.S. and the European models. While the European models had only two watch case forms and were produced in three metal variants (stainless steel, yellow gold, and red gold), there are more models of the U.S. Futurematics, and an additional case metal variant, 10 carat gold-filled stainless steel cases.