HP 39/40 series are graphing calculators from Hewlett-Packard, the successors of HP 38G. The series consists of six calculators, which all have algebraic entry modes, and can perform numeric analysis together with varying degrees of symbolic calculation. All calculators in this series are aimed at high school level students and are characterized by their ability to download (via cable or infrared) APLETs or E-lessons. These are programs of varying complexity which are generally intended to be used in the classroom to enhance the learning of mathematics by the graphical and/or numerical exploration of concepts.