  In this letter we describe the ground-state magnetic structure of the highly
anisotropic helimagnet Cr$_{1/3}$NbS$_2$ in a magnetic field. A Heisenberg spin
model with Dyzaloshinkii-Moriya interactions and magne- tocrystalline
anisotropy allows the ground state spin structure to be calculated for magnetic
fields of arbitrary strength and direction. Comparison with magnetization
measurements shows excellent agreement with the predicted spin structure.
