I still remember flashbulbs, flashcubes, and the early, all manual electronic flashes. Using these often resulted in the photographer’s question: did it trigger? And even if, the flashlight often made us look like white ghosts or dark shadows against the wall. At a given film speed and flash guide number (the maximum amount of light that the flash is able to burst off) the estimated flash-to-subject distance and the aperture were the only means of regulating the flash exposure.
Why am I bringing this up? To name the strong and weak points of the transceiver system, it is fitting that I should briefly explain the techniques and acronyms of the modern system flashes.