The SEPC result object plots the percent error in structural energy norm. The approximations of mesh discretization error associated with a solution are calculated for analyses having structural degrees of freedom. These structural approximations are based on the energy error (which is similar in concept to the strain energy) and represent the error associated with the discrepancy between the calculated stress field and the globally continuous stress field (see POST1 - Error Approximation Technique in the Mechanical APDL Theory Reference). This discrepancy is due to the assumption in the elements that only the displacements are continuous at the nodes. The stress field is calculated from the displacements and should also be continuous but generally is not. If the energy error is a significant portion of the total energy, then the analysis should be repeated using a finer mesh to obtain a more accurate solution. The energy error is relative from problem to problem but will converge to a zero-energy error as the mesh is refined.