It serves as the reference for identifying the place values of the digits. In a place value number system, digits have different values depending on where they are in relation to the decimal point. If there is no decimal point, its position must be assumed. The usual convention is that the decimal point is assumed to be located to the right of the rightmost digit. Example 123 = 123.0 There are other kinds of place value systems that do not use a decimal point. Examples 12:23 could be HH:MM or MM:SS. Either way, the number on the left has a value 60 times that on the right. VI versus IV The placement of the "digit" I before the higher order digit "V" means it is subtracted, rather than added. 
