def t90_from_t68(t68):
    """
    Converts IPTS-68 temperature to International Temperature Scale 1990
    (ITS-90) temperature.  This conversion should be applied to all in-situ
    data collected between 1/1/1968 and 31/12/1989.

    Parameters
    ---------
    t68 : array_like
          in-situ temperature [:math:`^\circ` C (ITPS-68)]

    Returns
    -------
    t90 : array_like
          in-situ temperature [:math:`^\circ` C (ITS-90)]

    References
    ----------
    .. [1] International Temperature Scales of 1948, 1968 and 1990, an ICES
       note, available from http://www.ices.dk/ocean/procedures/its.htm
    """

    return t68 * 0.999760057586179