public double getCloseValue(int series, int item) {
        double result = Double.NaN;
        Number close = getClose(series, item);
        if (close != null) {
            result = close.doubleValue();
        }
        return result;
    }

    /**
     * Returns the volume-value for one item in a series.
     *
     * @param series  the series (zero-based index).
     * @param item  the item (zero-based index).
     *
     * @return The volume-value.
     *
     * @see #getVolumeValue(int, int)
     */
    public Number getVolume(int series, int item) {
        return this.volume[item];
    }

    /**
     * Returns the volume-value (as a double primitive) for an item within a
     * series.
     *
     * @param series  the series (zero-based index).
     * @param item  the item (zero-based index).
     *
     * @return The volume-value.
     *
     * @see #getVolume(int, int)
     */
    public double getVolumeValue(int series, int item) {
        double result = Double.NaN;
        Number volume = getVolume(series, item);
        if (volume != null) {
            result = volume.doubleValue();
        }
        return result;
    }

    /**
     * Returns the number of series in the dataset.
     * <p>
     * This implementation only allows one series.
     *
     * @return The number of series.
     */
    public int getSeriesCount() {
        return 1;
    }

    /**
     * Returns the number of items in the specified series.
     *
     * @param series  the index (zero-based) of the series.
     *
     * @return The number of items in the specified series.
     */
    public int getItemCount(int series) {
        return this.date.length;