A. Lange & Söhne

I understand that the current 1815 Up/Down is based on early Lange pocket watches with a power reserve indicator. What seems odd is that on the pocket watch the "Ab" is at the high end of the scale (numerically speaking) and the "Auf" at the bottom. On th...  

Actually, there is even closer to the original... This one. ...  

...the fact that the power reserve dials show the number of hours of power remaining, but one runs from Ab to Auf and the other from Auf to Ab. It's as if the fuel gauge in one car ran down from Full to Empty and in another from Empty to Full!

From the watch, AB is marked red. It is in many watches marked red for "low" Thus a good guess tells me that "AB" is an abbreviation for empty. And thus "AUF" to represent full. In that case, for the watch, the gauge could be interpret as no of hours left... 

but my observation is that in pocket watches and specifically observation watches, the indication shows the number of hours the watch is running and not the reserve (how long the watch still can run). Afaik, the only current watch that has the same approa... 

So perhaps on the pocket watch the hand moves clockwise and shows elapsed time, and on the 1815 it moves anti-clockwise and shows the hours of reserve remaining. That's pure guesswork, but it seems plausible. How odd.

"All has an end only a sausage has two!" ... that was a very popular German song of the eighties. What it is meaning in this case is that you can pick what end you like. Technically I do not see any difference as the pr indicator moves from a higher hour ...