private void Overall_Usage_Btn_Click(object sender, RoutedEventArgs e)
{
TimeSpan usage = watcher.UsageTimeForGivenTimeframe(startTime, startTime + TimeSpan.FromDays(1));
MessageBox.Show(usage.ToString(), "Overall usage", MessageBoxButton.OK,
MessageBoxImage.Information, MessageBoxResult.OK, MessageBoxOptions.DefaultDesktopOnly);
}