The A. Lange & Sohne 1815 Rattrapante Perpetual Calendar watch. Model Reference 421.025FE. The new 1815 Rattrapante Perpetual Calendar was the first wristwatch from Lange combining the split-seconds and perpetual calendar complications. It has a beautiful movement – caliber L101.1 – complete with 636 individual parts. The split-seconds mechanism has two individual column-wheels – one for the chronograph and one for the rattrapante – and just like on the existing Lange Double-Split, the rattrapante is activated by the button at 10 o’clock. The perpetual calendar mechanism consists of 200 of the 636 components and will not need to be reset until the year 2100 – when the traditional leap year schedule is thrown off and the calendar will need to be advanced by one day – done by the push of one button. All of this is housed in the 41.9mm platinum case surrounding a silver dial on a black crocodile strap with a platinum deployant buckle. Truly a beautiful work of art and once you turn it over, you will get lost in the movement and understand why this is one of their sought after pieces. The watch comes in original packaging, with a set of documents.