apply it as in typing someone? I can get a tentative guess based on the felt "essence" (Fi+Ne; there is a reason this type is called the empath, as well as for the corresponding descriptions) given my experience of people with the type, and reading the type descriptions. Over time, of course, it gets better. I don't consider this a final typing of course if I don't know them. If I do know them and they are interested, I let them type themselves by introducing them to what I think might be their type (after all they do ask me what I would type them).