Rollei and Zeiss Ikon
10 and 9 researched events on one shared scale. Rollei 1920–present, Zeiss Ikon 1926–present.
The axis stretches where either maker has research and collapses where neither does, so a year sits opposite the same year on both. Event counts differ because research depth differs, not because one company did less.
Rollei1920–present · 10 events
Zeiss Ikon1926–present · 9 events · 5 concurrent threads
Read either maker on its own: Rollei · Zeiss Ikon