A logical value is a single character (1 or 0) enclosed in apostrophes.
Logical values are often used as a switch to represent a condition
such as on or off, yes or no, and true or false. When used in expressions,
a logical value can be optionally preceded by *NOT or 
. The following are examples of logical values:
| Constant | Value | Meaning |
|---|---|---|
| '0' | 0 | Off, no, or false |
| '1' | 1 | On, yes, or true |