1990 325i clock

Clock might be wrong term. The instrument on dash to right of radio that has

6 buttons. What is this and how does it work? Sometimes it displays the time (correctly I might add) and sometimes it displays the outside air temp (also correctly). But I can't switch between them and sometimes it is just flashing strings of numbers. What does memo do? How do I reset this instrument. Now it is displaying temp in centagrade not faranhite like before. Please enlighten me as this is my first BMW and am still learning its idiosyncrocies. Thanks Rick Burton