# Bijective Numeration - The Bijective Base-10 System

The Bijective Base-10 System

The bijective base-10 system is also known as decimal without a zero. It is a base ten positional numeral system that does not use a digit to represent zero. It instead has a digit to represent ten, such as A.

As with conventional decimal, each digit position represents a power of ten, so for example 123 is "one hundred, plus two tens, plus three units." All positive integers which are represented solely with non-zero digits in conventional decimal (such as 123) have the same representation in decimal without a zero. Those that use a zero must be rewritten, so for example 10 becomes A, conventional 20 becomes 1A, conventional 100 becomes 9A, conventional 101 becomes A1, conventional 302 becomes 2A2, conventional 1000 becomes 99A, conventional 1110 becomes AAA, conventional 2010 becomes 19AA, and so on.

Addition and multiplication in decimal without a zero are essentially the same as with conventional decimal, except that carries occur when a position exceeds ten, rather than when it exceeds nine. So to calculate 643 + 759, there are twelve units (write 2 at the right and carry 1 to the tens), ten tens (write A with no need to carry to the hundreds), thirteen hundreds (write 3 and carry 1 to the thousands), and one thousand (write 1), to give the result 13A2 rather than the conventional 1402.

The system of common numerals used in ancient Greece prior to the Hellenistic Age was a bijective base-10 number system in which letters of the Greek alphabet were assigned values between 1 and 900. This was the system used to reckon the year based on the four-year Olympiads, so for instance 480 BCE (the date of the Battle of Thermopylae) would be written ἔτει αʹ Ὀλυμπιάδος οδʹ, that is, the 1st year of the 74th Olympiad. These numbers are still commonly used in Greece for ordinals.