Left: distribution of heliocentric distance of the LAMOST OB star sample. Right: Relative distance uncertainty (﹩{\sigma }_{d}/d=\mathrm{ln}10\times {\sigma }_{\mathrm{log}d}﹩) as a function of distance. Only results for single stars are shown. The solid line delineates the median value of the relative distance uncertainty at various distances. The dashed line delineates the relative distance uncertainty in the case where only the Gaia parallax is adopted to infer the distance. The improvement to distance estimates using the spectroscopic ﹩{M}_{K{\rm{s}}}﹩ is clearly visible for distant stars.