A. Lange & Söhne

PeterCDE
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That´s a good point, i think

G'day,

the absolute difference is interesting, although it would need to break it down to the movement height (the "Up&Down" is a little larger, so the case may require a higher back for stability).
In any case, the way the power reserve indication is done implements limited space:

"A special variation of the UP-and-DOWN display was chosen for the 1815 UP and DOWN by Lange. It is based on a patent granted to Otto Lange in 1940 for his method of integrating a planetary gear train between the movement plates."
Lange website

And here´s a drawing of the 1943 patent, which may visualize it´s done by means of a small gear train "within" the gears and plates:



This may allow for a guess; the satellite wheels actually are pretty small and available space is scarce, so it´s not easy to produce them and not easy to assemble these pieces. Just that one doesn´t notice easily when looking at the movement or the dial.

The same applies to the "Lange 31"; that "Up&Down" indication makes use of 48 individual parts.
Of course that´s a much larger movement, but given most available space is occupied by the barrels and the escapement with remontoir, the gear drive and parts for the power reserve itself are pretty small.

So doing it in a way that does not affect the height of the watch very much is in fact a little challenge.

Cheers,

Peter