Sign Condition
The sign condition determines whether or not the algebraic value of an arithmetic
expression is less than, greater than, or equal to zero. The general format
for a sign condition is as follows:
General Format:

General Rules:
- When used, "NOT" and the next keyword specify one sign condition that defines
that algebraic test to be executed for truth value; for example, "NOT ZERO"
is a truth test for a nonzero (positive or negative) value. An operand is
positive if its value is greater than zero, negative if its value is less
than zero, and zero if its value is equal to zero. The arithmetic expression
must contain at least one reference to a variable.
ZEROS or ZEROES can be used instead of ZERO in a sign test.