Temperature determination of the narrow-lined stripped B star (top) and broad-lined Be star (bottom) from ionisation equilibrium. Markers indicate the MAPE values averaged over all measured EW ratios. For the narrow-lined star, this comprises EW ratios of Si III over Si II lines and Fe III over Fe II lines. For the Be star, results are shown for the EW ratio of Mg II over He I lines. Values for model spectra of varying surface gravities are indicated with different colours (see legends). With an estimated value of logg in the range 2.0–2.5 for the narrow-lined star, the best fit in terms of minimal MAPE is achieved for effective temperatures between 13 and 14 kK. For the Be star with estimated surface gravity in the range 3.5–4.5, the best fit is found for effective temperatures between 16 and 19 kK.