Uu is the long labial vowel and the sixth letter of the Ranjana order, the long member of the pair whose short member is U. It is made in the same way, the back of the tongue raised towards the soft palate and the lips rounded, and held about twice as long, and as with the other pairs the difference is not decorative but distinguishes words. With uu the varnamala completes its three pairs of simple vowels: a and aa in the neutral position, i and ii at the palate, u and uu at the lips. Everything that follows in the vowel series is of a different kind, either a liquid treated as a vowel or a vowel formed by combining two others, so uu marks the end of the plainest part of the inventory. In writing, the mark for uu sits beneath its consonant in the same position as the mark for u, distinguished by its form.
The independent letter shown here is used where the vowel opens a word. Sanskrit uses long uu in a good many common words and in a number of grammatical endings, so the mark is not rare, and it is one of the shapes a learner meets in the first days of study rather than something met later among the exceptions. The symmetry of the three pairs is worth noticing as a piece of design. Each pair occupies one place of articulation, each is written with its mark in one region of the syllable, and each is recited as a unit, so the learner acquires the sound, the position and the drawing together rather than as three separate lessons. That economy is what allows the varnamala to be taught to children by voice before any of it is taught by hand.