To begin a simulation, drag the bob up or down to compress or stretch the spring. When it is satisfactorily positioned press "Go". You may change the mass, m, of the bob or the Spring Constant(stiffness), k, by typing values in the appropriate fields before hitting "Go". Subsequent simulations will be plotted in different colors so that they may be compared. (Note the effect of changing m, k, and initial amplitude on the frequency) Pressing "Reset" will clear all old plots.