RangeOnly - script and chart function
                RangeOnly() is a dual function that returns a value if the expression evaluates to one unique value. If this is not the case then NULL is returned.
Syntax:
RangeOnly(first_expr[, Expression])
Return data type: dual
Arguments:
The argument of this function may contain inter-record functions which in themselves return a list of values.
- first_expr: The expression or field containing the data to be measured.
 - Expression: Optional expressions or fields containing the range of data to be measured.
 
Examples:
| Example | Result | 
|---|---|
| RangeOnly (1,2,4) | 
                                 Returns NULL  | 
                        
| RangeOnly (5,'abc') | Returns NULL | 
| RangeOnly (null( ), 'abc') | 
                                 Returns 'abc'  | 
                        
| RangeOnly(10,10,10) | Returns 10 |