Patent No. 9349 was granted to A. Lange & Söhne on 18 May 1879. The subject was a “device in pocket watches for recognising whether the watch is wound or unwound and for indicating how much time remains before it reaches the totally unwound state.” This was the official moment of birth of Lange’s characteristic UP/DOWN power-reserve indicator. The name suffix of the 1815 UP/DOWN makes this clear.

Just like the UP/DOWN power-reserve indicator, the blued hands, the recessed central segment, the Arabic numerals and the railway-track minute scale were inspired by historic pocket watches. A top-mounted wheel train on the caseback side of the movement and two additional screwed gold chatons are manifestations of the mainspring barrel that was enlarged in comparison with the 1815 and delivers power for three days.