Graphical displays of past and future levels of drugs may be a useful adjunct to manual dosing. We have previously found that a display of predicted future values speeds step changes in end-tidal sevoflurane. In this study anaesthetists made step changes of 0.3% in effect site sevoflurane, with and without the display and as increases and decreases. We analysed 91 changes. When the predictive display was present, users made larger vaporiser dial changes of 3.9% vs 3.1% (95% CI for the difference -1.3% to -0.01%, p = 0.046) reflected in larger end-tidal changes (95% CI for the difference -0.009 vol% to -0.34 vol%, p = 0.06). There was no difference in the speed of change (220 vs 227 s (95% CI for the difference -51 to 32 s)), or in the accuracy of the change. In this study the predictive display influenced the magnitude of the step changes made by anaesthetists but did not affect the speed or overall accuracy of the change.