Why is a change in dry mass of an organism the best indicator of growth?

Actually, dry mass is a more reliable measure of mass than fresh mass because the former excludes the fluctuating water concentrations in the biological material measured which is present in the latter. Actually, dry mass, the mass of a biological sample after the water content has been removed, usually by placing the sample in an oven. The dry mass is used as a measure of the biomass of a sample.