Since every nc word is composed of a letter and a value. Before we begin a serious discussion of the meaning of nc programming words we need to consider the meaning of value within the interpreter. A real_value is some collection of characters that can be processed to come up with a number. A real_value may be an explicit number (such as 341 or -0.8807), a parameter value, an expression, or a unary operation value. In this chapter all examples will use explicit numbers. Expressions and unary operations are treated in the computation chapter. The use of parameter values or variables are a described in detail in the Using Variables chapter.

EMC uses the following rules regarding numbers. In these rules a digit is a single character between 0 and 9.

A number consists of :

- an optional plus or minus sign, followed
- by zero to many digits, followed, possibly, by
- one decimal point, followed by
- zero to many digits provided that there is at least one digit somewhere in the number.

Some additional rules about the meaning of numbers are that:

- Numbers may have any number of digits, subject to the limitation on line length.
- A non-zero number with no sign as the first character is assumed to be positive.
- Initial and trailing zeros are allowed but not required.
- A number with initial or trailing zeros will have the same value as if the extra zeros were not there.