The perk says that if you repair a weapon with a repair kit it has 10% stronger attack until it becomes too damaged. So this should mean that if my sword has 50 attack it will have 55 if my bow has 60 it will have 66 and so on. The problem is that it doesn’t just apply individually to the specific weapon. Each weapon you have equipped (this includes your shield as you repair it with a blacksmith kit) increases the damage of not only itself, like it is meant to, but your other weapons as well.
Sword Equiped
-Sword Attack: 115 115 5
Sword and Bow Equpped
-Sword Attack: 125 125 6
-Bow Attack: 74 (normally 68)
Sword, Bow, and Shield Equipped
-Sword Attack 135 135 6
-Bow Attack 80