Calibrator I-189-A is a range calibrator for pulse-triggered range oscilloscopes. The oscilloscope sweep is triggered at approximately 480 cycles per second (cps), and the range is calibrated by direct comparison with 500-yard calibration markers. The unit is a portable, self-contained instrument. It contains a crystal-controlled, 327.80-kilocycle (kc) oscillator which furnishes the 500-yard markers and the 480 cps synchronising pulse outputs. Two coaxial cables for connecting the instrument to the set to be calibrated are provided.