How can I make a skill that adds a % of damage to a normal attack?

[Dwarfio]

I just realized that a skill I made to deal a bit of extra damage will not level with my character, and will eventually become useless. My first thought was to just make multiple skills with the same name and remove the useless skill and add a more powerful one after a few levels, but I just wanted to know if there's and easier way, like just making a skill that deals an extra % of your basic attacks damage.

 

[kire]

You can use the atk up skill but that raises all of you attack, tough