Patek Philippe & Co., Genève

18k, damascened nickel lever movement, stamped twice with the seal of Geneva, 18 jewels, mono-metallic compensation balance, precision regulator, adjusted to heat, cold, isochronism and 5 positions, black dial, applied baton and square numerals, subsidiary seconds, circular case with semi-hooded stepped lugs, case, dial and movement signed, accompanied by an Extract from the Patek Philippe Archives.

The accompanying Extract from the Patek Philippe Archives confirms that this watch was manufactured in 1942, left the factory with a black dial and was sold on July 28th the same year.   

Patek Philippe commenced production of the reference 540 in 1937.