If I understand correctly you need something like

deltapercent= mypercentfunction(0ldvalue,newvalue, abval )

you also need business rules, is an increase in a debt to be reported as an increase, or a decrease? so a third parameter, abval can be passed


FUNCTION mypercentfunction
lparameter Oldvalue, newvalue, abval

IF oldvalue = newvalue
return 0
endif

IF oldval=0 .and. abval
return 100
endif
IF oldval = 0 .and abval < 0
return -100
endif
IF abval
delta=(abs(oldval)*100 - abs(newval))*100 )/abs(oldval
* multiply by 100 first to increase accuracy of rounding !
return delta
endif



you probably need to add soem more conditions , too !

not an easy task, given how math challenged most clients are !