def get_meas_sds_index_tuples(update_info):
    """Index tuples for meas_sd.

    Args:
        update_info (pandas.DataFrame): DataFrame with one row per Kalman update needed
            in the likelihood function. See :ref:`update_info`.

    Returns:
        ind_tups (list)

    """
    ind_tups = []
    for period, meas in update_info.index:
        ind_tups.append(("meas_sds", period, meas, "-"))
    return ind_tups