Hello Zig,
I think that you are referring to the altitude setting panel (FHIS) which is not included in 35J. When you pulled the knob the FHIS panel showed “PLANE” and the horizontal crossbar would (theoretically) indicate glide path to the base. According to one of the Draken pilots that I talked to, this function was practically never used. The panel was removed in the 35J modification.
Cheers /Thomas