The "detent" action was actually caused by the 15 coil pins engaging the 15 contacts which provided the positive feel of the catacomb "locking" into position.
Since the NC-100 was intended for the SWL or intermediate-level ham, a different type of signal strength or tuning indicator was utilized.
The NC-100 Series "MOVING COIL" Receiver production spanned from 1936 up to 1949. Certainly the design of the "MOVING COIL" method for band change used in the NC-100 receivers impressed the commercial operators of the late thirties with modified versions being ordered by the Bureau of Air Commerce and the CAA for use in airports around the country (even as late as post-WWII.) The NC-100XA version impressed the U. Navy who ordered special versions with low Local Oscillator radiation that became the famous RAO family of WWII receivers.
Even post-WWII buyers could still purchase the descendants of the NC-100 in the modernized NC-240D receivers.
The front of the coil catacomb had a "track" machined into it and the band change shaft, which also carried a pinion gear, protruded beyond the pinion gear and rode in this "track," thus supporting the front of the catacomb.
The rack gear was mounted to the front of the catacomb at the proper level to engage the pinion gear to allow moving the catacomb via the band changing shaft.