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Why does postAtTime not trigger at the right time when screen is turned off
static long second, ticker, uptimemilli;
onCreate() {
  second = ticker = 0;
  Handler mHandler = new Handler();
  uptimemilli = SystemClock.uptimeMillis();
  mHandler.postAtTime(mUpdateTimeTask, uptimemilli+1000*ticker++);
}

private Runnable mUpdateTimeTask = new Runnable() {
  public void run() {
    if (second == 100)
      return;
    UpdateMyTextView(second++);
    if (second%10 == 0)
      PlayBeep();
    mHandler.postAtTime(mUpdateTimeTask, uptimemilli+1000*ticker++);
  }
};