 Other applications included early television systems, where the various line and frame frequencies were kept synchronized by pulses included in the video signal.The first multivibrator circuit, the classic astable multivibrator oscillator (also called a "plate-coupled multivibrator") was first described by Henri Abraham and Eugene Bloch in "Publication 27" of the French "Ministère de la Guerre", and in "Annales de Physique 12, 252 (1919)".Since it produced a square wave, in contrast to the sine wave generated by most other oscillator circuits of the time, its output contained many harmonics above the fundamental frequency, which could be used for calibrating high frequency radio circuits.