The terminology in the UK differs in some respects from the above description: The production control room is called a "gallery", a mobile production truck is called an "OB van" or a "scanner" (a BBC term). In UK television practice, the technical director is the senior technical person in the gallery and supervises the technical team, but does not operate the "vision mixer". The TD is responsible for ensuring that the gallery is technically fit for purpose, the routing of internal and external sources, as well as liaison with other technical areas such as master control rooms and transmission suites. They may additionally perform vision control duties, matching the exposure and colour balance of the cameras ("racking").