A new technique for improving the precision of measurements of SUSY particle masses at the LHC is introduced. The technique involves kinematic fitting of events with two fully identified decay chains. We incorporate both event ETmiss constraints and
independent constraints provided by kinematic end-points in experiment invariant mass distributions of SUSY decay products. Incorporation of the event specific information maximises the information used in the fit and is shown to reduce the mass measurement uncertainites by ~30% compared to conventional fitting of experiment end-point constraints for the SPS1a benchmark model.
