Explanation: RADAR determines range by precisely measuring the time delay between transmitting a pulse and receiving its echo. This time measurement is critically dependent on the accuracy of the sweep and timing circuits within the RADAR indicator. If these circuits are miscalibrated or faulty, they will incorrectly convert the measured time delay into a displayed range, leading to an inaccurate reading. * **A) Check the sweep and timing circuits:** This directly addresses the fundamental mechanism of range calculation. A fault in these circuits is a direct cause of an incorrect range indication, making this the most effective way to identify the faulty RADAR. * **B) Triangulate target using GPS and visual bearings:** While this method could provide an external verification of the target's true range, it doesn't diagnose the internal fault in the RADAR unit itself. It requires external tools and conditions. * **C) Check antenna parallax:** The physical separation of two antennas on a vessel results in a negligible range difference for practical targets and would not cause a significant discrepancy or make one RADAR "incorrect." * **D) Use the average of the two indications:** Averaging an incorrect reading with a potentially correct one only yields an inaccurate average and does not identify or correct the underlying fault in the malfunctioning RADAR.