This calculator is kind of different. Entry is done RPN style, so if you've only ever used an algebraic calculator you might have a short learning curve ("1 + 2 =" in RPN is "1 [enter] 2 +"). Also, it uses RPN to build expressions, not just do calculations, which is a little different than the way HP calculators worked (it's arguably much better - but some people just want what they know). On the other hand, if you're willing to try something different, this calculator does a pretty good job of combining the elegance of RPN with the friendliness of the best algebraic calculators. Features: - Completely free with NO ADS (there is an optional donation in the main menu) - Enter commands using GUI or keyboard - Graphs functions, data sets, and linear regressions and finds roots, intersections, and local min/max - Powerful and elegant functional programming (see the online help to learn how it works) - Use lists to work with multiple numbers or expressions at one time - Exact mode (e.g. sqrt(8) = 2*sqrt(2) , 1/2 + 1/3 = 5/6) - Numerical integration and differentiation - Extensive online help