String summarizePerformanceSince(ApdexData since) {
    long total = myTotalCount - since.myTotalCount;
    long sluggish = mySluggishCount - since.mySluggishCount;
    long slow = getSlowCount() - since.getSlowCount();

    if (sluggish == 0 && slow == 0) return "ok";

    if (slow == 0) return sluggish + "/" + total + " sluggish";

    return sluggish + "/" + total + " sluggish, " + slow + "/" + total + " very slow";
  }
String summarizePerformanceSince(ApdexData since)