What's the difference between a diverter and a rough-in valve?

[Iculus]

My question is whether there is any real difference between the functioning of a diverter and rough-in valve piece. As I understand it, a diverter is the piece which "diverts" the water between one and three different water outlets. If that's so, then doesn't a rough-in valve function similarly? I've heard the rough-in valve described as the "engine" of a bath or shower. Some clarification between these two terms would help a lot. Thanks!

 

[IFIXH20]

A diverter valve do not have a true off position -- A rough-in tub/shower valve will have a true off position.

 

[AQualityPlumber]

A shower valve is responsible for temperature control. A diverter is just what it says, diverts water from one shower head to another. Volume controls are simple on and off valves.