A semi-automatic transmission is in which some of the operation is automatic (generally the actuation on the clutch), but the driving force's input is required to move off from the standstill or to change gears. This kind of gearbox doesn’t have fixed gears, but instead utilizes a technique of pulleys https://stephenqrokf.bloggactivo.com/33417098/new-step-by-step-map-for-automobile-gearbox