Sum of EWs of the He I λ 4471 line and the He II λ 4541 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 sum of EWs for a non-rotating model with the same stellar parameters is indicated with the horizontal dashed line and simulated 1σ and 3σ error bars are indicated. The left y-axis indicates the sum of the EWs while the right y-axis indicates the corresponding helium abundance.