Futurebasic/Language/Reference/on overflows

Description
This statement designates a particular function or subroutine as an overflow handling routine. An overflow handling routine is called in response to any math operation involving a division by zero, or any floating-point math operation that results in a number larger than FB can handle. If you don't designate any overflow handling routine, FB will attempt to continue evaluating the expression, but the resulting number is unpredictable.