A simple regression against colors of Landolt stars yields: (V-R) = 0.508(B-V) + 0.040 or: R = V - 0.508(B-V) - 0.040 Note that the sign difference on the zero-point is opposite what Arne posted, which was my arithmetic error, not his. This relation works quite well for stars bluer than B-V = 1.2. More complex functional forms were derived by John Caldwell and published in the South African Astronomical OBservatory Circulars a few years ago. These cover all the UBVRIJHK, uvby, and DDO colors with extended range in color space. \Brian