Abstract: An apparatus for measuring phase and amplitude jitter and simultaneously and audibly counting and monitoring transient excursions of two linear bar-chart type readouts calibrated in degrees and modulation percents and which are capable of displaying jitter measurements. The transient excursions in the form of phase hits, gain hits, drop outs and impulse noise are simultaneously counted in parallel registers and means are provided for visually indicating the cumulative real time count total of each register in numerical display. The method of evaluating parameters affecting voiceband data transmission includes simultaneously displaying phase and amplitude jitter components onto linear bar-chart displays and separately deriving the information for each of said displays and providing continuous and sequential illumination on each display encompassing the range of fluctuations from the jitter detectors.