The article treats the subject of function approximations for a computer's built‐in library as a typical topic for a school mathematical laboratory. Following a brief description of how such a laboratory is envisaged as part of mathematical education, approximation by interpolation is discussed at the pre‐calculus level. Special attention is given to the removal of ‘black box’ procedures, and inherent concepts such as quality of approximation, relative error and computational efficiency are examined. Suitable examples are given, demonstrating the actual construction of library functions.