The Hewlett-Packard Model 8556A Spectrum Analyzer LF Section covers the frequency range from 20 Hz to 300 kHz. When it is combined with an IF Section and a Display Section it functions as the tuning section of a low frequency spectrum analyzer. The analyzer electronically scans input signals and displays their frequency and amplitude on a CRT. The horizontal, x-axis, is calibrated in units of frequency and the vertical, y-axis, is calibrated in absolute units of voltage (µV, mV, dBV) or power (dBm). Therefore, absolute and relative measurements of both amplitude and frequency can be made.