  Different choices of the renormalisation scale (muren) can be used to
describe hard scattering processes with two jets at large transverse momentum
in deep-inelastic scattering at HERA by fixed order perturbative QCD
calculations.
  For leading (LO) and next-to-leading order (NLO) calculations the simplest
choices, Q2, the virtuality of the incoming photon, and the mean squared
transverse momenta of the two jets ET2, are studied in different kinematic
regimes.
  It is found that only if both Q2 and ET2 are large, the NLO calculation is
stable with respect to numerical variations of muren while the LO calculation
strongly depends on it. If only one of the two scales, either Q2 or ET2, is
large, the NLO is more stable than the LO calculation, but exhibits
nevertheless a strong residual scale dependence.
  When both scales are relatively small, large scale dependencies are found in
both cases. Moreover, large differences between the LO and NLO calculation are
found.
  Generally, the use of ET2 as renormalisation scale is favoured over Q2, since
scale dependencies are less pronounced and NLO corrections are smaller.
