The tetradecimal (base-14) positional notation system is based on the number fourteen. Comparatively, the decimal system is based on the number ten, the hexadecimal system is based on the number sixteen, and so on. Other names used for the base-14 system include quadrodecimal and quattuordecimal (although these terms can be confused with quaternary which is a base-4 notation system).
Tetradecimal requires fourteen symbols. Since there are only ten common decimal digits, the notation can be extended by using letters A, B, C and D to represent values 10, 11, 12 and 13, respectively. For example, decimal values 0 to 20 in tetradecimal would be: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, 10, 11, 12, 13, 14, 15, 16. The tetradecimal number 373 would be 689 in decimal.
This numeric base is infrequently used. It finds applications in mathematics as well as fields such as programming for the HP 9100A/B calculator, image processing applications and other specialized uses.