public void RecordTime()
        {
            var existent = TimeRecordsInternal.SingleOrDefault(x =>
                (x.Number == CurrentNumber) && !x.IsPossiblyWrong);
            if (!ReferenceEquals(null, existent))
            {
                var message = string.Format(
                    "Number {0} was already recorded at {1}!", existent.Number, existent.Time);

                MessageBox.Show(message, "Warning", MessageBoxButton.OK, MessageBoxImage.Warning);

                return;
            }

            var record = new TimeRecord(++_id, CurrentNumber, DateTime.Now);
            TimeRecordsInternal.Add(record);
            _haveUnsavedData = true;

            NotifyOfPropertyChange(() => CanSearch);
        }