Electromagnetic type curves are basic tools in mining geophysics in reducing ambiguity of interpretation. To this end, a mathematical solution is given for the quasi-static response of an infinitely conducting disk in a dipolar magnetic field. The solution, which emerges as a series solution of Laplace's equation in oblate spheroidal co-ordinates, converges rapidly enough only in certain ranges of radii of the disk. Sommerfeld's image method leads to an alternate solution that is exact. For finite conductivity, the mathematics becomes rather unwieldy, so experimental modelling produced the type curves in this range. By using high frequencies and aluminum disks, “infinitely” conducting models were constructed to check the theoretical solutions. All computation was done on an IBM 650 digital computer.