Retails for $120.00.  HP-20S Scientific calculator.  A comprehensive scientific calculator, the Hewlett-Packard HP20S features easy-to-use algebraic entry and a built-in program library of over 100 scientific and mathematic functions. The library has frequently used functions like root finder, Simpson's rule of integration, complex number operations, 3x3 matrix operations, quadratic formula, and curve-fitting programs--all at the touch of a key. The HP20S also has essential trigonometry and math functions such as sine, cosine, tangent, exponential, and natural log and antilog functions.