  We make use of twisted boundary conditions for off-shell Rome-Southampton
renormalisation. This allows to define the vertex function precisely, at a
fixed physical momentum that need not be one of the Fourier modes of a
simulation. This definition includes choosing the orientation with respect to
lattice axes, and so lattice artefacts including ${\cal O}(4)$ breaking then
have a valid Symanzik expansion. Excellent statistical precision is afforded by
volume plane-wave sources, enabling both a theoretically and statistically
clean continuum limit to be taken. Thereafter all $p^2$ dependence can be
unambiguously identified as continuum anomolous running.
  The use of non-exceptional momenta has been found to greatly reduce the
dependence of non-perturbative vertex functions on both mass and $p^2$. We
illustrate how this can be developed into a practical scheme for step-scaling
the RI/SMOM approach with initial results. The size of the possible steps is
continuous, rather than discrete allowing one to take arbitrarily small steps,
and the scheme inherits from RI/MOM the property that it is easy to implement
for general operators.
