@staticmethod
def pair_method(obsHistID, snid, maxObsHistID):
    """
        Combine the obsHistID and snid to form a single index.

        Parameters
        ----------
        snid : int, `np.ndarray`
            unique ID representing each object
        obsHistID : int, `np.ndarray`
            unique ID representing a pointing
        maxObsHistID : int (scalar)
            max value of obsHistID
        """
    return snid * maxObsHistID + obsHistID
