When you either learn or test your skillz, it should be written in which stack the flashcard is at the moment. That would make it easier to maybe tolerate small errors from your side.
Example,
the right answer is "school"
but you spelt it "shool" if the the flashcard is in stack 1, maybe you can tolerate that and move that to stack two and make a mental note that it's spelt school and focus your effort on learning more words, But if it's in stack 2 or three or whatever you might be more restrictive and maybe move it backwards a stack...
just my two cents.
Example,
the right answer is "school"
but you spelt it "shool" if the the flashcard is in stack 1, maybe you can tolerate that and move that to stack two and make a mental note that it's spelt school and focus your effort on learning more words, But if it's in stack 2 or three or whatever you might be more restrictive and maybe move it backwards a stack...
just my two cents.