In later years, to make a distinction, masu became written as '枡' by attaching the left radical of tree (木) to '升,' but in reality, the distinction between 升 and 枡 seems to have been not so strict.
後に容器の方は「升」に木篇をつけて「枡」と書き分けるようになったが、実際にはあまり区別されていなかったようである。