Degree sign

Angles, temperatures and latitude all share this small raised ring: 45°, 21 °C, 36° N. One theory traces it to a raised zero in the base-60 arithmetic of ancient astronomers, the same system that splits each degree into 60 minutes.

Two other characters look almost identical. Spanish and Portuguese use the masculine ordinal indicator º in abbreviations such as 1º, and there is also a ring diacritic, ˚. For measurements, the degree sign is the correct choice.