The containment set as an extension of the range of a function has been introduced in a series of white papers; see e.g. Walster, G. W.: Closed Interval Systems, Sun Microsystems, 2002, and Walster, G. W, et al.: Extended Real Intervals and the Topological Closure of Extended Real Relations, Sun Microsystems, 2002. The containment evaluation provides an exception free evaluation of functions over an arbitrary range. In this paper we discuss alternative existing implementations (C++ Interval Arithmetic Programming Reference, Sun Microsystems, 2000, and Hofschuster, W. et al.: The Interval Library fi_lib++ 2.0, Design, Features and Sample Programs, Universitat Wuppertal, 2001) of the power function, introduce a new version, develop containment sets and discuss algorithms for the implementation.