Contemporarily with joining the Ebauches SA, FHF and Landeron merged around 1925, but remainded fairly independent. The production of the FHF 2124 was passed to Landeron in the 50s, and the Landeron 2124 appeared in registers since 1961 (Bestfit).
www.ranfft.de
•Note the different pallet cock?
It is usual for there to be a stamp depicting the calibre under the balance or perhaps under the dial. Not that this is an absolute.