  We present very accurate individual masses (1.2% relative accuracy) for the
two components of Gl 570BC, an interferometric and double-lined spectroscopic
binary system. They were obtained from new high accuracy radial velocity and
angular separation measurements, analysed together with previously published
measurements. From those data we determine a much improved orbit through a
simultaneous least square fit to the radial velocity, visual, and parallax
information. The derived masses and absolute magnitudes generally validate the
theoretical and empirical mass-luminosity relations around 0.5 Msol, but point
towards some low level discrepancies at the 0.1 to 0.15 magnitude level.
Forthcoming results of this observing program will extend the comparison to
much lower masses with similar accuracy.
