KenK, I do hope you mean your thumb NAIL

! Anyway your reply is the closest to what i use but i use a plastic pen and hold the knife at app. 45 degree angle to test the edge then reverse the pen & knife position so as to test "both" sides of the edge. Like the thumb nail it should not slip or its not sharp. Thing is I just recently learned this method from the internet and thus I'm not sure just how good it works so I thought i'd compare the methods here with this one.