Where can I get a guide to the use of IOP of Gaussian98?

 As I just learned,
 adding IOP(5/13=1) which allows the SCF to print
 out the MO's even in the event that convergence was not reached.
there are also some other IOP functionality I know,like Fock Matrix : iop(5/33=3)
 Overlap Matrix : iop(3/33=1)
But how are these lines interpreted and where how do I know what kind of combination generates what kind of functionality.Is there any guide or tutorial on this?I would be very interested.
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