A. Lange & Söhne 1815 40 Platinum 233.025

Otherwise it is the same watch as the yellow gold 1815 40 (233.021) and the pink gold 233.032: 40 mm across, 8.9 mm thick, Arabic numerals, alpha hands and the calibre L051.1. The platinum case and the 500-piece run are what set it apart, as the gold versions are not limited. Sotheby's describes a sapphire display back held by six screws, so the movement is on show. The case takes a 20 mm strap.

For platinum with a different face, the 1815 200th Anniversary F. A. Lange (236.049) is also a 40 mm platinum 1815 on the L051.1, with a black dial and a run of 200. The 1815 Annual Calendar (238.026 in white gold, 238.032 in pink gold) keeps the 40 mm diameter but moves to the L051.3, which adds a power reserve indicator, in a 10.1 mm case.