Experimental resistance versus temperature plots measured in various magnetic fields up to 7 T in strength are presented for highly oriented YBaCu oxide thin films deposited onto crystalline zirconia. Possible broadening mechanisms are summarised and a detailed analysis made for three models which involve processes intrinsic to the ideal superconducting material. It is shown that two distinct potentials may be needed to understand flux pinning in different temperature ranges below Te. These two potentials have quite different temperature and field dependence.