Aerosonic 4 inch, mechanical, cockpit clock. This type with the multi functions has the distinction of NEVER having been figured out by ANY pilot. I have never spoken to one pilot who knows how to operate all of the weirdo knobs properly. If you are the exception, let us know. We'll give you "on screen credit". Ops checked, very rare, often the first thing stolen from an aircraft being torn down...(we bought these).