Em space(em quad): A fixed amount of white space equals to that of the type size used;that is ,a 10-point type ,10-point em is 10 points wide.The space will not be altered for justification purposes as will a space band.

• 正方空位（正方空铅）:一个固定的空位，它相等于所用的字大小。例如10点字，它的“正方空位”的阔度是10点。这个空位在齐行调整时不能像“空位楔”的作更改。