Help me please,

I am not able to add an additional trend for this wonderful library ControlP5 Chart, original sample chart having two trends  and I want to add one more, this is what I have added in the ControlP5chart.pde

for (int i=0;i<f.length;i++) {
    f[i] = random(30, 70);
}
myChart.updateData(2, f); // I assumed 2 is an index of the trend

Failed with error: IndexOutOfBoundsException: Index:2, Size:2