  The 900 ORCs of Mathewson, Ford & Buchhorn which were folded by Persic &
Salucci (astro-ph/9502091) are analysed. A technique for removing that part of
an ORC most dominated by the central region it introduced (see astro-ph/0107300
for a far more comprehensive discussion of this).
  The analysis then shows that a power-law model of the form V = A R^b, where
the parameters (A,b) differ between ORCs, provides an extremely good
description of the generic behaviour of ORCs when these central regions are
removed.
  It is shown that a very powerful correlation exists between the free
parameters (A,b), and that parameter A can be very accurately modelled in terms
of the luminosity properties of galaxies.
  The net conclusion is that the power-law model is, at the very least, an
extremely good first-order model for the behaviour of disc dynamics in the
outer regions of ORCs.
