The mantissa stands for a mathematical notation of exponential values. In exponential notation, the mantissa is the factor that precedes the power of ten of another base. It, the mantissa, indicates the valence.exponent. The mantissa of 24.87 x 10exp12 is 24.87, the base is the number 10, and the exponent is 12. If the number 0.0034 is written exponentially, then you get 3.4 x 10exp-3. The mantissa is 3.4, the base is 10, and the exponent is -3.