private double[][] ticks(double start, double end) {
   LinearTickMarkCalculator c = new LinearTickMarkCalculator();
   Axis axis =
       new Axis() {
         private static final long serialVersionUID = 1L;
       };
   axis.setStart(start);
   axis.setEnd(end);
   double[][] data = c.calculateTickMarks(axis);
   return data;
 }