Through numerical investigations, various examples of the Duffing type forced spring equation with epsilon positive, are studied. Since [epsilon] is positive, all solutions to the associated homogeneous equation are periodic and the same is true with the forcing applied. The damped equation exhibits steady state trajectories with the interesting property that these steady states are periodic of period 2[pi]/[omega] and coincide with the harmonic trajectory of the undamped equation. This is a case of a limit cycle for a non-autonomous equation. Student computer laboratory investigations and research problems arise naturally and several are suggested.