180/Historical Note

Historical Note on $180$
There are $180^\circ$ in a straight angle.

Thus the colloquial expression doing a $180$, meaning turning completely around (either literally or metaphorically) to face in the opposite direction, can be found in a variety of contexts.

$180 \, ^\circ \mathrm F$ is the number of degrees Fahrenheit between the melting point ($32 \, ^\circ \mathrm F$) and boiling point ($212 \, ^\circ \mathrm F$) of water.