What is the quantity aspect of the interval between fx4 and a4?

your word would be isle.

isle is an island or peninsula especially a small one.

if you add the letter "a" you get aisle, which is a passage between 2 rows of something like chairs, shelves, or something else.

мвнгм реозж рнрнзн оло пщмть яшрврн эёъдb шпмъч хпмщзц эьшрг тьи гау.