An operating number, also referred to as an Imperial code name, a call number, or as a TK number, was the alphanumeric code by which personnel of the Galactic Empire, including stormtroopers and officers, were identified. The operating numbers of officers consisted of three letters followed by two numerals, like LRC-01, or three letters and three numerals, like ISB-021. Those of stormtroopers consisted of two letters followed by three or four numerals, as exemplified by LS-005, TK-626, MB-223, TK-421, and TK-5331. Generally speaking, a low number was an indicator of high rank.