The Unary Minus Priority box on the Model Generator tab:

is used to set the priority of the unary minus operator.   The two available options are High and Low.

There are two theories as to the priority that should be assigned to the unary minus (i.e., negation) operator in mathematical expressions.  On the one hand, there is the Excel practice that the unary minus operator should have the highest priority, in which case, the expression -3^2 would evaluate to +9.  On the other hand, there is the mathematicians’ preference for assigning a lower priority to unary minus than is assigned to exponentiation, in which case, -3^2 evaluates to -9.  Note that regardless which relative priority is used, one can force the desired result through the use of parenthesis.

LINGO defaults to the Excel approach of setting a higher priority (High) on negation than on exponentiation.