The Tektronix Type P plug-in is a step response calibrator for 500-series scopes. It applies a step signal to the vertical input (plug-in connector pins 1 and 3) of the scope. The step is generated by a mercury switch in the Type P and it has a 4 nanosecond risetime. The Type P is designed to simulate a Type K plug-in being driven by a Type 107 pulse generator. In this sense, it is designed to act as a standard, not as an ideal square pulse source. Why is this preferable to calibrating the mainframe using a square pulse? Would the high-frequency components of a square pulse cause problems?