In this book, magnetic measurements are discussed much wider than just obvious testing of magnetic materials or the measurement of the magnetic £eld. Direct and indirect measurements of magnetic parameters like magnetic £eld strength H, ‘ux density B, permeability μ, susceptibility χ, or magnetostriction λ are commonly used in other areas of science and technology, such as paleomagnetism, magnetoarcheology, mines detection, displacement or proximity testing, current measurement, nondestructive testing of materials, and medicine diagnostics, to name just a few. The practical applications of magnetic measurements are almost unlimited. For example, the magnetostriction sensors can be used for testing exotic quantities such as acidity pH, blood coagulation, concentration of castor oil (ricin), or even presence of Salmonella bacteria.