Levels of Distractibility: Who Cares? = *. Some people will be distracted from your meaning: = **. Many people will be distracted from your meaning: = ***.
Question: I always get "further" and "farther" mixed up. I know that one means distance and the other means additional, but which is which?
Answer: When I'm talking I mix them up also. They sound too much alike. You're right: "farther" means distance: "He walked farther down the hall." "Further" means "additional," as in "I have nothing further to say." Keeping them straight in writing shouldn't be a problem. You can always look them up again. But speaking.... Think of the FAR in "farther."
Rating of Distractibility: In writing, (***). In speaking, (**).