I still remember when I was in primary school, pupils are not allowed to use calculator because this is the time when we are being taught how to manually compute equations either by using our mind or by using paper and pencil to solve number problems. Even in high schools, the uses of calculators are limited and are still frequently prohibited unless it is really necessary to compute the log, cosine values and the likes.
These are all part of our training to understand the concept of mathematics and to know by heart how to add, subtract, multiply, divide, compute fractions, percent and decimals. These long years of training are really evident because I noticed that people who are in high school stage are extremely bright. They are fast thinker and can manually solve equations almost instantly.
The freedom of using calculators are best experienced in college days, here we can almost compute anything and everything using the calculator, perhaps because we are already solving complex equations. And now with the advent of Internet technology, we now have almost all kind of calculators that you could use online.
My favorite online calculator is the Calculator.com. It has several kinds of calculator like fraction calculator, percent calculator, area calculator, temperature calculator and even graphing calculator. This site also have calculator for computing loans and mortgages making this calculator great for college students as well as people who occasionally need to calculate for something.