  Among the sources of systematic error in nucleon structure calculations is
contamination from unwanted excited states. In order to measure this systematic
error, we vary the operator insertion time and source-sink separation
independently. We compute observables for three source-sink separations between
0.93 fm and 1.39 fm using clover-improved Wilson fermions and pion masses as
low as 150 MeV. We explore the use of a two-state model fit to subtract off the
contribution from excited states.
