To begin a simulation, drag the bob left or right to establish the initial angle. When it is satisfactorily positioned press "Go". You may change the length, the mass of the bob or constant of gravitational accleration, 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 length, mass, gravity, and initial amplitude on the frequency) Pressing "Reset" will clear all old plots.