Dash Insert drop-down menu. Dash The dash is a punctuation mark that is similar in appearance to and , but differs from these symbols in both length and height. The most common versions of the dash are the en dash (–), equal to half the height of the font; the em dash (—), twice as long as the en dash; and the horizontal bar (―), whose length varies across typefaces. Historically, the names of en dash and em dash were loosely related to the width of a lower-case "n" and upper-case "M", respectively, in commonly used typefaces. Usage varies both within
Two-man rule Two-man rule The two-man rule, also known as the four-eyes principle, is a control mechanism designed to achieve a high level of security for especially critical material or operations. Under this rule all access and actions require the presence of two authorized people at all times. Per US Air Force Instruction (AFI) 91-104, "the two-person concept" is designed to prevent accidental or malicious launch of nuclear weapons by a single individual. In the case of Minuteman missile launch crews, once a launch order is received, both operators must agree that it is valid by comparing the authorization code in the