What if the exponent is already very large, like 99? Then we are in trouble since we cannot add 1 to the exponent without overflowing it. When this happens we signal overflow and stop the computation:

           0.56740 x 1099                                OVERFLOW!
     +     0.48293 x 1099
     --------------------
           1.05033 x 1099            --->????          0.10503 x 10100

In the notation we are using in this chapter, we can only store 2-digit exponents, so we would have to signal an overflow if it ran into 3 digits. The same sort of thing happens with underflow, when the two exponents are negative and near the smallest allow exponent.