Instruments for measuring voltages include the voltmeter, the potentiometer, and the oscilloscope. An octopus circuit can be used to demonstrate the waveform images on an oscilloscope. The dual-beam analog oscilloscope can display two signals simultaneously. Special high voltage probes form compensated attenuators with the oscilloscope input. This is the principle applied in compensated oscilloscope probes to increase measurement bandwidth. This oscilloscope, refined and developed by Tektronix, was the model 511. The detected signal was intended to be displayed on an oscilloscope. This allows the use of standard oscilloscope probes. A cathode-ray display, made from an oscilloscope, was used to show range information. This output line was connected to an oscilloscope. The "Z" name refers to the characteristic impedance of the oscilloscope and cable. The range of frequencies an oscilloscope can usefully display is referred to as its bandwidth. CH output was read with an oscilloscope. A phase comparison can be made by connecting two signals to a two-channel oscilloscope. There are programs which allow a sound card to be used as an audio-frequency oscilloscope.