function on_frame() {
                if (that.execution_timer_id != -1) {
                    return;
                }
                window.requestAnimationFrame(on_frame);
				if(that.onBeforeStep)
					that.onBeforeStep();
                that.runStep(1, !that.catch_errors);
				if(that.onAfterStep)
					that.onAfterStep();
            }
Starts running this graph every interval milliseconds.
@method start
@param {number} interval amount of milliseconds between executions, if 0 then it renders to the monitor refresh rate