def units_conversion(units_id='SI'):
    """Computes the units conversion from SI units used internally to the
    desired display units.

    Parameters
    ----------
    units_id: str
        String variable identifying units (English, SI) SI is the default.

    Returns
    -------
    units: dict
        dictionary of unit conversion and labels
    """

    if units_id == 'SI':
        units = {'L': 1,
                 'Q': 1,
                 'A': 1,
                 'V': 1,
                 'label_L': '(m)',
                 'label_Q': '(m3/s)',
                 'label_A': '(m2)',
                 'label_V': '(m/s)',
                 'ID': 'SI'}

    else:
        units = {'L': 1.0 / 0.3048,
                 'Q': (1.0 / 0.3048)**3,
                 'A': (1.0 / 0.3048)**2,
                 'V': 1.0 / 0.3048,
                 'label_L': '(ft)',
                 'label_Q': '(ft3/s)',
                 'label_A': '(ft2)',
                 'label_V': '(ft/s)',
                 'ID': 'English'}

    return units