Spectral Induced Polarisation (SIP) is an extension of Induced Polarisation (IP), being itself an extension of DC-geoelectric. SIP measures the frequency-dependent (i.e. spectral) complex impedance, equivalent to the amount of resistance and phase shift between electrical current and voltage. The usual frequency range is tens of kHz to mHz. The advantage over DC-geoelectric is the additional information gained. Research aims at distinguishing material properties, salinity and saturation. Besides geoelectrical use it is also applied to building materials.