The input system of an oscilloscope contains a certain amount of resistance shunted by capacitance. This is called the input impedance of the oscilloscope. To the input impedance of the oscilloscope is also added the capacity of the test leads. This total shunting capacitance and resistance, when connected across a high impedance, high frequency, or broad band width circuit, may be sufficient to detune the resonant circuit or to load the test circuit and seriously distort the waveforms under observation. For this reason a low capacity (high impedance) probe is used to isolate the input of the oscilloscope from the circuit under test when waveforms are to be observed in any audio, video, sweep or sync circuit.