This leaflet briefly refers to generic documents concerning values for voltage at the OHL and voltage tolerances and then defines an index of the quality of voltage at (the) pantograph(s) (for categories of high speed line). When dimensioning studies for electric traction fixed installations are carried out, mainly on the basis of simulated traffic, this index called the "mean useful voltage at train pantographs" is calculated using a formula which can be adapted to dedicated software. It reflects the level of performance that electric traction fixed installations can provide to different trains running in a given zone. Compliance with the minimum values indicated in the leaflet will enable infrastructure managers to guarantee a realistic simulation of the traffic graph. Lastly, the leaflet contains a method to verify that simulation results converge with measurements on board trains.