Gaisser, T.K.; Hillas, A.M. (1977). "Reliability of the method of constant intensity cuts for reconstructing the average development of vertical showers". Proc. of 15th Int. Cosmic Ray Conf., 13–26 Aug 1977. Vol. 8. Plovdiv, Bulgaria. p. 353. Bibcode : 1977ICRC....8..353G.