public String askVWAP() {
    Vector<Double> vals = new Vector();
    
    for(int i = 0;i < ROWS;i++) {
      if (!asks[i].isEmpty()) {      
        // String s = "";
        // for (String key : asks[i].keySet()) {
        //   s += " " + key + "=" + asks[i].get(key);
        // }
        // System.out.println(s);
        
        vals.add(new Double(asks[i].get("price")));
        vals.add(new Double(asks[i].get("size")));
      }
    }
    
    return String.valueOf(Calc.vwap(vals));
  }