Image illustrating the different hyphens, en-dashes and em-dashes could be more helpful edit
In the page on the Dash, In the earlier part of the article it states:
"The most common versions of the dash are the en dash (–) and the em dash (—), named for the length of a typeface's lower-case n and upper-case M respectively."
Then later in the article: "The widths of en and em dashes have also been specified as being equal to those of the upper-case letters N and M respectively,[8][9] and at other times to the widths of the lower-case letters."
The image should show lowercase n,m and uppercase N M.
