The masses of nuclei from n to Ca41 have been derived from nuclear Q values exclusively, without recourse to mass spectrometric results, by an approximate least-squares adjustment. Main results are:(1) The comparison of the value of the mass difference 2D2-He4 derived from nuclear data with that from mass spectrometric data furnishes the most accurate experimental verification of the relation E=mc2. The accuracy of this verification is 1/6000.(2) Tables are given for the most probable mass values from nuclear data of the 79 nuclei from n to Ca41. Fundamental mass differences are n-H1=0.7824±0.001Mev, n+H1-D2=2.2255±0.0015Mev,2H1-D2=1.4431±0.0018Mev, 2D2-He4=23.840±0.004Mev. Mass values include n=1.008 9842(±17),H1=1.008 1440(±17),D2=2.014 7381(±29),He4=4.003 8732(±21),C12=12.003 807(±5),S32=31.982 188(±26),Ca40=39.975 204(±39) (3) The result of the present calculation demonstrates that the method used by the author, within the limitations of present-day nuclear experiments, has the same significance as an overall least-squares adjustment, attains same degree of accuracy, but is simpler in procedure and more convenient in the examination of the experimental results for systematic errors.(4) Comparison of nuclear results with recent mass spectrometric results shows that the masses of H1 and D2 are in agreement for the two systems, but definite discrepancy exists for C12 and much larger ones for S32 and Ca40.