Stutter Boxes

[dsm4g63]

I have heard alot of ppl talking about stutter boxes and just had a few questions about them:

What is a stutter box is it strictly electronic or is it mechanical,
I know they hold your engine at a consistent rpm is that all they do?
any other points or comments..

thanks
gary

 

[Goblin]

http://www.tmo.com/prod/eprom/drag.shtml