This passage is incorrect regarding the trautonium:
"Its ribbon virtual control surface allows all kind of glissando a Theremin or an Ondes Martenot would allow, though the sensored ribbon is much more precise than the tube full of graphite[dubious – discuss] used as a variable resistance in the Trautonium"
The trautonium ribbon was a "spirally twisted length of nickel-chrome resistance wire -- this is the grid bias resistor of the thyratron" (Journal of the Audio Engineering Society, Volume 2; p.149, 1954)
The trautonium's oscillator, driven by a Thyratron Tube, has its pitch set by pressing this biasing resistor against a metal plate (ibid).
Graphite, a material used in modern membrane switches (used in ribbon controllers) was not employed in the ribbon of any trautonium known to this author.
Lorin Edwin Parker Professor, Audio / Electronic Music Art Institute of California, Los Angeles