R′ _UV vs. R′ _HK plots of our volume-limited Hipparcos sample. The left panel, a log plot, shows the correlation between R′ _FUV and R′ _HK. The solid line represents the fit given by Equation (8). The right panel, a linear plot, shows that R′ _NUV measurements are very noisy with many negative values. The ellipse shows the median errors. The distribution of R′ _NUV is centered on zero.