Dynamic access to the numerical properties of the implementation can enable the development of portable numerically robust software. Fortran 90 provides such access through a combination of a model of the methods for approximating real values and a set of corresponding intrinsic functions for extracting model values. These intrinsic functions, of which there are a total of 16, are called the environmental inquiry (nine) and numeric manipulation (seven) intrinsic functions.
Each kind of real number is modeled by
where