Explanation: Radar systems measure distance (range) by timing how long it takes for a transmitted pulse to travel to a target and return. Range rings on a radar display are generated by a highly stable oscillator that produces precise timing pulses after the main transmit pulse. Each pulse corresponds to a specific range increment, creating concentric circles that represent known distances from your vessel. If the **Range ring oscillator** (A) is inaccurate, the timing pulses it generates will be incorrect. This means the displayed range rings will be drawn at distances that do not correspond to their labeled values, leading to an erroneous indicated distance to any target, including a lighthouse. * **Video amplifier (B)** affects the strength and clarity of target echoes, not their measured distance. * **STC (Sensitivity Time Control) (C)** adjusts receiver gain to reduce clutter from close-in targets but doesn't impact range measurement accuracy. * **FTC (Fast Time Constant) (D)** helps reduce rain clutter and sharpen target echoes, but it doesn't affect the fundamental timing for range calculation.