ABS returns the absolute value of a number.
SGN returns a value indicating the sign of a numeric expression (1 if the
expression is positive, 0 if it is zero, or -1 if it is negative).
 
ABS(numeric-expression)
SGN(numeric-expression)
 
    - numeric-expression    Any numeric expression.
 
Example:
    PRINT ABS(45.5 - 100!)           'Output is:  54.5
    PRINT SGN(1), SGN(-1), SGN(0)    'Output is:  1  -1  0