Java timer/benchmarker

public class NanoTimer{

    private long    start;
    private long[]  data    =new long[100];
    private int     pos     =99,count;
    private boolean started =false;

    public void start(){
        started=true;
        start=now();
    }

    public void end(){
        if(!started) throw new IllegalStateException("Not started");
        pos=(pos+1)%100;
        data[pos]=now()-start;
        if(count<100) count++;

    }

    public double msAvrg100(){
        long sum=0;
        for(int i=0;i<count;i++){
            sum+=data[i];
        }
        return toMs(sum/count);
    }

    public double ms(){
        return toMs(data[pos]);
    }

    private static long now(){
        return System.nanoTime();
    }

    private static double toMs(long nano){
        return Math.round(nano/10000D)/100D;
    }

}