1899 J. Wardle 45 Platen knob, for turning the Platen..either backward or forward.
1928 M. Crooks xvii. 125 The student can be trained to get the right amount of ‘flick’ with the platen knob to enable the paper to enter the machine up to whatever writing point is desired.
1987 81 8 Roll platen knob till paper is through to top.