6B codes

6B codes refer to navigation equipment. Most flying timepeices including stopwatches were 6B coded as they were considered navigation tools. The most desirable being the 6b/159 pilots/navigators wristwatch, see earlier threads on these watches. 6B will also be found on a range of other items such as ICAN computors, compasses, even pencils and pencil cases carried 6B codes if they were intended to be used by navigators.
hope this helps.