 Due to the need of a simple to operate and solid locomotive, the "Chemins de Fer de l'État" even went to choose the pressure of the boiler (or "timbre" in French).The pressure was 12 kp/cm² or 12 "hectopièzes" (old units of measurement, 1.2 MPa in modern units), this enabled to machine to develop an output of at 60 km/h and at 100 km/h.From 1932 the "timbre" was increased to 14 kp/m² to obtain a power of at 60 km/h and at 100 km/h; locomotives were recoded from "B" to "C" as this work was done.