Can anyone tell me what addon this is?

[GND95 0]

So I was watching a vanilla youtube pvp video and this guy has an addon that places numbers inside his hotkeys that gives an estimate of how much damage the particular spell will do. Does anyone know which addon this is? I know there is one for TBC and above clients that is called "Dr. Damage" but I don't believe that addon exists for vanilla. I'll include a screenshot to give you guys an example of what exactly I'm talking about. The screenshot may be a bit hard to see but here is a link to the youtube video I was talking about: https://www.youtube.com/watch?v=zNg9po5YIQA

 

Thanks in advance!

 

 

[Barrymanalow 1]

TheoryCraft

[GND95 0]

Thank you very much!