Eurocode steel designers will be well aware of Mcr, – it must be calculated en route to the lateral torsional buckling resistance. Formulas exist for simple situations, but for more complex arrangements, software is the way forward. SCI has just completed a significant upgrade of the assessment tool on steelconstruction.info which has now been released. The new version allows full flexibility to define supports, restraints and loading to reflect complex arrangements. Intermediate supports and restraints may be defined at any position along the member, at a user-defined position from the shear centre. Point loads, distributed loads and moments may also be applied at any position, as illustrated below. This gives the user the means to assess a member with a non-standard loading arrangement, perhaps with intermittent restraints to (for example) one flange only. To assess this type of complex arrangement, software is the only realistic option. Members may be UB or UC, or defined by dimensions or by properties, so fabricated sections may be modelled. Defining members by dimensions allows the user to assess tapered members which vary in height over the length of the segment. Comprehensive output is reported, which may be printed or exported to other applications. This new tool is freely available at www.steelconstruction.info.