A surface profile measuring instrument (1), and method, for measuring the surface profile of a substrate (13). The surface profile measuring instrument (1) comprises an electromagnetic probe (8), the electromagnetic probe (8) comprising a probe tip operable to be brought into proximity with a surface of a substrate (13) to be measured, a drive unit (2) operable to generate a low frequency magnetic field penetrating the surface of the substrate (13), a pick up unit (3) operable to detect the strength of the magnetic field and output a magnetic field strength reading and a computation unit (4) operable to determine a surface profile measurement based on the magnetic field strength reading.