Level and impedance adjustment can be achieved by adding a potentiometer or adjustable resistor. The joystick potentiometer acted as a variable resistor in the RC network. Variable resistors, such as the potentiometer and the rheostat, have ohmic characteristics. Resistor trimmers generally come in the form of a potentiometer (pot), often called a trimpot. Instruments for measuring voltages include the voltmeter, the potentiometer, and the oscilloscope. The term "rheostat" is becoming obsolete, with the general term "potentiometer" replacing it. It acts as an analog potentiometer upgradable digitally. An adjustable potentiometer inside the system controlled the volume of the internal speaker. The device is operated by a foot treadle that opens and closes a potentiometer. The selected step on the ladder determines the resistance ratio of the digital potentiometer. Volume control in an audio device is a common application of a potentiometer. A multiplying DAC used as a digital potentiometer can eliminate most of these limitations. The level control is usually a rotating potentiometer (called a "pot"). Its operation is similar to the original potentiometer. They suffer from wear and electrical noise in the potentiometer track.