One of the problems that many mathematics and science departments confront is accounting for all of the scientific calculators they lend to students. Like textbooks no matter how diligent a school is in tracking how many are lent out, one or two always seem to disappear by the end of the year. Also like textbooks there are some good and free alternatives to buying scientific calculators. Here are some that you can try.
Desmos offers a fully functional, browser-based graphing calculator. The calculator performs all of the functions you would expect to see in a graphing calculator with a couple of extras that you don't find in typical graphing calculators. Desmos allows you to share your equations and graphs through a Bit.ly link. Desmos graphs your equations as you type them and redraws them as you alter your equations. And because it is written in HTML5 Desmos works on your iPad.
Microsoft Mathematics 4.0 is a graphing calculator that plots in 2D and 3D. Of course, the calculator does many other functions such as solving inequalities, converting units of measure, and performing matrix and vector operations.
Calkoo is a website that offers forty-three free online calculators for a variety of functions. The list of calculators that Calkoo is divided into ten categories. Those categories are mathematics, measurement & conversion, saving & investing, capital budgeting, cost of capital, wages & taxes, financial analysis, health, loan & leasing, and stock analysis.
Encalc is a free online scientific calculator. Encalc describes itself on its homepage as follows, "Encalc is an online scientific calculator. Its strength lies in its ability handle units and dimensional analysis, to define variables and its large database of constants. Parenthesis and scientific formulas are also supported." One of the features that I really like about Encalc are the explanations of how different variables and constants function within an equation or formula. Encalc can be embedded into your blog or website too.
Web2.0calc is a free online scientific calculator. While it won't replace the TI-85, it can do what your average high school student needs it to do. The best part is, you don't have to use it on the Web2.0calc site because they offer three widgets that you can use to embed the calculator into your own blog or website.
Speed Crunch is a free scientific calculator application for Windows, Mac, and Linux operating systems. Speed Crunchperforms all of the functions necessary for high school Algebra and Geometry courses except graphing. In addition to performing all of these functions, Speed Crunch has a "math book" containing commonly used equations and formulas. One Speed Crunch feature that appealed to me from a design standpoint is the color coding of equations to differentiate between constants and variables.
Graph.tk is a free online graphing utility that I found in the Google Chrome Web Store. Graph.tk allows you to plot multiple functions through its dynamically resizing grid. To graph an equation on Graph.tk just click the "+" symbol to enter a new equation. Click here to watch a short video of Graph.tk in use. One thing that the video doesn't show and isn't clear the first time you use Graph.tk is that you need to delete the existing default equations before you start.
Scientific Calculator is a Chrome web app that works offline and online. The calculator performs all of the functions that you would expect and it offers a couple of handy additional features. When it is connected to the web the calculator records your calculation history. Any scripts that you write in Scientific Calculator can be saved online and shared for use by others.