Can't adjust my 7850's Voltage?

[Archoson]

My favorite computer store in my country had a sale on the Sapphire HD 7850 1gb Edition, and since I am on a tight budget I jumped at the opportunity because I heard the Sapphire cards, and the 7850 in general overclock like beasts. But I can't adjust the voltage on my card, if I go to Asus GPU Tweak, there is no voltage meter, same with MSI. Why is there no voltage meter? =[

 

[wanderer11]

In afterburner you have to go into settings and check unlock voltage control.

 

[Archoson]

Already done, still can't adjust voltage.