Excel is "helpful" and tries to anticipate how you'd like the data to
display based on keystrokes you enter. When you got the displayed
result 13/02/1900 Excel thought you were entering a date, or perhaps
that cell was formatted as a date. That displayed output may also be
the result of a conflict between your computer's regional settings and
the type of data you entered.

What figure did you enter, and how is the cell formatted?