code: public void addMeasurement(long durationInMillis) {
      count.addAndGet(1);
      timerSum.addAndGet(durationInMillis);
      timerSumOfSquares.addAndGet(durationInMillis * durationInMillis);
    }
docs: Add a timer measurement for this timer.<br>
  The application decides which unit to use for timing.
  Milliseconds are suggested and some {@link ReportVisitor} implementations
  may imply this.
  @param durationInMillis