The Deep Inelastic Scattering 2+1 jet cross-section is a useful observable for precision tests of QCD, e.g. measuring the strong coupling constant s . A consistent analysis requires a good understanding of the theoretical uncertainties and one of the fundamental ones in QCD is due to the renormalisation scheme and scale ambiguity. Di erent methods, which have been proposed to resolve the scale ambiguity, are applied to the 2+1 jet crosssection and the uncertainty is estimated. It is shown that the uncertainty can be made smaller by choosing the jet de nition in a suitable way.