We aim to use the ENGIN-X facility to measure the residual field within an industrial scale (1 x 0.8 x 0.3 m), direct chill (DC) cast slab of a high strength, creep resistant magnesium rare earth alloy. The high temperature strength of the alloy has resulted in a significant level of residual stress driven (cold) cracking, within the cast slab. These measurements will be used for the validation of a finite element model of the DC casting process for this material. Such modeling is particularly challenging, requiring simulation of both thermal and mechanical properties of the solid, semi-solid and liquid phases of the alloy. Validation of the model will allow best practice casting parameters to be established. Furthermore, these measurements will be used as a benchmark to assess the applicability of a range of residual stress measurement methods to industrial scale problems.