def find_most_extreme_value(values):
    """
    Find the most extreme (signed) value and index of the value.

    Parameters
    ----------
    values: float array
        An array of signed values.

    Returns
    -------
    The value and index of the most extreme value.

    """
    max_value = values.max()
    min_value = values.min()
    max_value_index = values.argmin() if (max_value < -min_value) \
        else values.argmax()
    max_value = min_value if (max_value < -min_value) else max_value

    return max_value, max_value_index