PBP work with un-signed integer

Second-First=951-1423=-472

-472 will become 65064, wich is actually 65536 -472

if you want to test if your result is negative, you could still test the bit15 of the substraction
Code:
Result=951-1423
if result.15=1 then
    ' do the negative stuf here
    ELSE
        ' do the positive stuff here
    ENDIF