  An analytical method of calculating eddy current in a metallic spinning
gyroscope in external magnetic field is presented. With reasonable assumptions,
the problem is simplified from the time-dependent one governed by Maxwell
equations to the boundary value problem of Poisson equation, which yields a
closed form expression of the eddy current. The rotation frequency as a
function of time is calculated, compared with experiment and the relative error
is found to be 8.61%.
