This graphical tool shows the effect of non-proportional hazards or a missing covariate on the power of the proportional hazards regression model. One can manipulate the hazard functions using sliders to create different hazard ratios over time keeping either the final survival rates, the mean or the median constant. Further, one can alter the hazard ratio by not considering an important covariate. The power is shown for each hazard ratio function. The graphical user interface shows each hazard function, each survival curve and the hazard ratio.