I am not certain, but it appears to be similar to another keyboard I used to have and the dial when turned controlled sound volume.

http://support.dell.com/support/edocs/acc/P171818/multlang/QSG_DAO.pdf

This keyboard is shown here in the manual but the flat dial like button is not identified. 

Arnethedog, Thanks for the response. I am disappointed that the manual does not label this dial/button. Perhaps someone else will know exactly what this does. 

I believe the keyboard and mouse are bluetooth and I do

not think you will find that in the computer manual

you should have a large blue and white sheet  explaining  how to install the keyboard and mouse and its  functions

the silver knob is for volume and the keys surrounding it our multimedia keys

Bob Moyer

Bob, We did not have any problems setting up this keyboard and mouse. We just want to know what the black dial does. There is no silver knob on this particular model. It is a flat dial that blends into the same plane as the keyboard.