Myslite writes the consonant m and takes the numeral sixty. Its name is the plural imperative of the verb to think, think, and it is one of the letter names that make the recited alphabet read as a set of instructions rather than as a list.
The sound is a plain nasal and it is entirely stable across the history of Slavic, so the letter offers none of the evidence about sound change that the yus letters or the jers or yat provide. What it does offer is a very high frequency. Old Church Slavonic uses m in some of its commonest endings, and the letter appears many times on every page of a gospel manuscript, which makes it one of the signs by which a hand can most quickly be characterised.
The numeral sixty follows from counting the Glagolitic letters in their own order, this being the fifteenth sign.
In the angular Croatian hand the letter is one of the most distinctive shapes on the page, and it is among the forms that make a Croatian missal look at first glance like a different script from a Bulgarian gospel book rather than a later stage of the same one. Both are Glagolitic, and the change from one to the other happened gradually over several centuries in a tradition that never lost continuity with its own past.