The physical forms of instruments that could be called AGFM’s are diverse, as they have been used to study a range of samples under different conditions, and different geometries. A list of the instruments discussed in this section can be found in Table 2.1, along with details of the detection systems used, some design parameters, and the resolutions obtained. The first demonstration of resonant operation of a force magnetometer was by Zijlstra [3] in 1970.