Abstract: A real time electronic engine control system is disclosed and includes a method of an apparatus for preventing overflow during a fixed point arithmetic operation. Each of two input numbers is divided by the same fixed number to obtain quotients of the input numbers and the arithmetic operation is then performed on the quotients of the input numbers to obtain a resultant number. The resultant number r from the arithmetic operation is compared to maximum (p) and minimum (q) register overflow values and the value of r is selected if p>r>q, while the value p is selected if r.gtoreq.p, and q is selected if r.ltoreq.q. Finally, the selected one of the compared numbers is multiplied by the fixed number to provide the result of the computation.