In a pulse waveform, the interval between (a) the time, during the first transition, that the pulse amplitude reaches a specified fraction (level) of its final amplitude, and (b) the time the pulse amplitude drops, on the last transition, to the same level. Note: The interval between the 50% points of the final amplitude is usually used to determine or define pulse duration, and this is understood to be the case unless otherwise specified. Other fractions of the final amplitude, e.g., 90% or 1/e (where e = 2. 71828. . . ,) may also be used, as may the root-mean-square (rms) value of the pulse amplitude. Deprecated synonyms pulse length, pulse width. 2. In radar, measurement of pulse transmission time in microseconds, that is, the time the radar's transmitter is energized during each cycle.