im not sure i understand the picture. Doesnt tibia only make use of integers, thus, making the studded legs with arm 2, with an arm bonus of +29% make it round up to arm 3. Effectively making it arm: +50%? (new armor value 3)/ (old armor value 2) = 1.5
If the client made use of floats it would instead be 2.58 armor.
