For even more precise location mapping, two additional digits were proposed and ratified as an "extended locator", making it altogether eight characters long, and dividing "subsquares" into even smaller ones. Such precision has uses in very short communication spans. Beyond this, no common definition exists to extend the system further into even smaller squares. Most often the extending is done by repeating alternating subsquare and square rules (base numbers 24 and 10 respectively). However, other bases for letter encodings have also been observed, and therefore such "extended extended" locators might not be compatible.