What ↋ means
Base 12 uses twelve distinct digit values. Once those run out, the next number is written as 10, meaning twelve; ↋ marks eleven.
In 1860, Isaac Pitman published turned forms of 2 and 3 for the dozenal values ten and eleven. The Dozenal Society of Great Britain later promoted turned forms; American dozenalists used related designs created by W. A. Dwiggins. Unicode records one form without deciding every community's preferred design.
Using ↋ marks a numeral as dozenal for readers familiar with that system.
Don't confuse it with
2Questions people ask
1Why does ↋ show as a box on some devices?
Because that device's fonts have no glyph for it. The character is still correct and still copies correctly — the box is a missing glyph, not a broken character.
How to type ↋
↋\218BCodes and encoding1 code points
A visible symbol can contain several code points. JS .length counts UTF-16 units; UTF-8 counts bytes.