I emailed GEC and asked them the same Question. Answer came back- we cannot tell you, we sharpen all our knives by hand, we recommend keeping the angle as fine as possible. So i think 30 degrees inclusive should be fine. When i have to sharpen my latest purchase, i am going to mark the edge and try 15deg. per side. I asked them because i have just received my first GEC and did not want to stuff up the edge, wanted to keep it factory angle.