Analysis of information sources in references of the Wikipedia article "Rotary engine" in English language version.
In order to keep the engine running smoothly on reduced power settings, it was necessary for the selector switch to cut out all cylinders at evenly spaced intervals. It was also beneficial to have all cylinders firing periodically to keep them warm and to prevent the spark plugs from fouling with oil. The selector switch has five positions, zero (0) for off and four running positions, one through four (1-4) (see Photo 5). The Gnôme 9N had two magnetos (and two spark plugs per cylinder) and the selector switch was wired to the right magneto only, so it was necessary for the pilot to turn off the left magneto if he wanted to change the speed of the engine.
Le 6 juin 1905, Louis et Laurent Seguin fondent la société des moteurs Gnome à Gennevilliers
In order to keep the engine running smoothly on reduced power settings, it was necessary for the selector switch to cut out all cylinders at evenly spaced intervals. It was also beneficial to have all cylinders firing periodically to keep them warm and to prevent the spark plugs from fouling with oil. The selector switch has five positions, zero (0) for off and four running positions, one through four (1-4) (see Photo 5). The Gnôme 9N had two magnetos (and two spark plugs per cylinder) and the selector switch was wired to the right magneto only, so it was necessary for the pilot to turn off the left magneto if he wanted to change the speed of the engine.
