How accurately do we know the parameters of hot DA white dwarfs

We present new determinations of effective temperature, surface gravity, and masses for a sample of hot DA white dwarfs selected from the EUVE and ROSAT Wide Field Camera bright source lists in the course of a near-IR survey for low mass companions. Our analysis, based on hydrogen NLTE model atmospheres, provides a map of LTE correction vectors, which allow a thorough comparision with previous LTE studies.We find previous analyses underestimate both the systematic errors and the observational scatter in the determination of white dwarf parameters via fits to model atmospheres.