[计] 媒体用毕符

[化] 射气

Em \Em\, n. (Print.)
The portion of a line formerly occupied by the letter m, then
a square type, used as a unit by which to measure the amount
of printed matter on a page; the square of the body of a
type.

M \M\, n.
1. (Print.) A quadrat, the face or top of which is a perfect
square; also, the size of such a square in any given size
of type, used as the unit of measurement for that type:
500 m's of pica would be a piece of matter whose length
and breadth in pica m's multiplied together produce that
number. [Written also {em}.]

2. (law) A brand or stigma, having the shape of an M,
formerly impressed on one convicted of manslaughter and
admitted to the benefit of clergy.

{M roof} (Arch.), a kind of roof formed by the junction of
two common roofs with a valley between them, so that the
section resembles the letter M.