Explanation: A variable resistor, commonly known as a potentiometer, is the most typical component used for a panel control like a variable range marker. This component allows for the continuous adjustment of resistance in a circuit, which in turn controls voltage or current levels. For a "variable range marker," this adjustment would typically set a voltage threshold or amplitude that defines the marker's position, size, or intensity on a display (e.g., an oscilloscope, radar, or spectrum analyzer). By varying the resistance, the user directly controls the electrical parameter that dictates the range indicator. Variable inductances and capacitances are primarily used for tuning resonant circuits, such as in Variable Frequency Oscillators (VFOs) or filters, not for direct amplitude or range level control. A variable resolver is an electromechanical device for precise angular position sensing, far too specialized for this common control function.