Ratio of the EWs of the He II λ 4541 line to the He I λ 4471 line as a function of inclination for a 40 kK star at various inclinations, at various rotation rates. The rotation rate as a percentage of the critical rotation rate is indicated in the legend, with darker colors corresponding to lower rotation rates and lighter colors corresponding to higher rotation rates. The EW ratio for a non-rotating model with the same stellar parameters is indicated with the horizontal dashed line. Simulated 1σ and 3σ error bars are indicated based on a simulated S/N of 300 and R of 6700. The left y-axis indicates the ratio of the EWs while the right y-axis indicates the corresponding temperature.