Calculators are a necessary tool in science and math classes. But, they don't have to cost the students anything.
First, there are a ton of free calculator apps available for every smartphone (iOS, webOS, Android, BB, Windows) so any student with a smartphone or PDA can get one on there.
Second, there are some free downloadable calculators, such as Microsoft Math and most computers have a built in calculator.
But, free, online calculators are also a great resource for educators and students. There are calculator extensions for Chrome and Firefox that students can use on their computer or through their Google account.
Here are some free online calculators that I like:
Web 2.0 Calc.com - free online scientific calculator. Available on mobile browser. Can be embedded in your own website or blog too.
Math.com's online calculators - basic, scientific, square root, and more.
eCalc online calculator and math help - has an online calculator along with math help. There are also downloadable calculators, an iPhone app, iGoogle gadget, and embeddable widget for your site. There is also an unit conversion calculator.
Scientific Calculator - online scientific calculator that takes up whole web page. Makes it easier to read and use.
Save money and use free calculators instead of buying them!