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Left Flag
Right or "reversed field" flag
General David Petraeus
To wear our country's flag properly, the field of stars is worn closest to your heart. Further, when worn on the sleeve of a military uniform, the flag should appear to be advancing and not retreating. Thus, if your patch is to be worn on your LEFT sleeve, use a left flag (normal). For patches worn on your RIGHT sleeve, use a "right" or "reversed field" flag.
Since the Flag Rules do not specifically address the positioning of the patch, a decision is left to the discretion of the organization prescribing the wear. Some elect to use the "left" flag on both sleeves. [Note: many states and cities have ordinances pertaining to the use of the flag; you may wish to contact the Attorney General of your state or the City Attorney's office regarding this matter.] If you are planning to wear only one patch, it is recommended that you wear a "left" flag on your left sleeve.
Military guidelines specify that in support of joint or multi-national operations (as in Iraq), the "right" flag is worn on the right sleeve (see picture), 1/4" below the shoulder seam or 1/8" below any required unit patches. (Class A uniform excepted.)
Some people find the "right flag" disrespectful of the flag and some are calling it the "wrong flag." They seek to gain support to encourage a change in the regulations to always use a "left flag" even on a right sleeve.