"Since Gilbreth died, chronocyclegraphs have been very little used by other motion study experts. Alford, in his "Production Handbook" published in 1945, lists the chronocyclegraph among present day research techniques, but most other writers only refer to it as one of Gilbreth's experiments."
"We have no specifications for Gilbreth's apparatus, but from the photographs shown in Fig. 25, it is obvious that his early apparatus embodied a tuning fork as the interruptor of the electric supply. The bottom photograph shows an apparatus embodying a disc commutator. (...) As the disc revolved, each contact engaged a stationary contact finger connected to a resistance, so arranged that first four, then three, and then two contacts were linked, the circuit being broken completely on the last contact, making the light progressively dimmer, until it went out altogether.
"The disc had two series of these contacts, and revolved at five, ten, or fifteen revolutions per second, by means of a pair of stepped pulleys, driven by a belt from an electric motor. It gave lights blinking at 10, 20 or 30 times per second.
"This apparatus was noisy and cumbersome, but its chief disadvantage was that because it functioned by delaying the extinguishing of the lamps, it was only possible to increase the speed of the flashes at the expense of the intensity of the light. This caused difficulty in photographing anything but the very shortest cycle, except in almost total darkness.
"Also, because of the interruption of the current, the intensity of the light must always fall below the maximum for the same lamp on uninterrupted current, since the disc was liable to stop at a point where the maximum current could reach the lamps. It was therefore unsafe to use more than the nominal amount of current recommended for the lamp employed."
Deac Rossell (email@example.com)