Bisection with Rate of Convergence

private static void bisectionMethod(double a, double b) {
        double tol = 0.0000001;

        List<Double> pastValues = new ArrayList<Double>();

        double fa = funct(a);
        int counter = 1;
        while(Math.abs(b-a) >= (tol)) {

            double m = (a+b)/2;
            pastValues.add(m);
            double fm = funct(m);
            if((fa*fm)<=0) {
                b=m;
            }else {
                a=m;
            }
            if(pastValues.size() < 4) {
                System.out.println(counter + ": Interval = [" + a + ", " + b + "] x = " + m);
            }else {
                double y0 = Math.log(Math.abs(pastValues.get(pastValues.size()-1) - pastValues.get(pastValues.size()-2)));
                double x0 = Math.log(Math.abs(pastValues.get(pastValues.size()-2) - pastValues.get(pastValues.size()-3)));
                double y1 = x0;
                double x1 = Math.log(Math.abs(pastValues.get(pastValues.size()-3) - pastValues.get(pastValues.size()-4)));
                double roc = (y1-y0)/(x1-x0);
                System.out.println(counter + ": Interval = [" + a + ", " + b + "] x = " + m);
                System.out.println("Rate of Convergence = " + roc);
            }
            counter++;
        }
    }