Scientific Calculator

Although there's several calculator widgets existing, I still feels that my widgets has some advantages: 1. standard and scientific mode 2. Designed using pure HTML, not graphics, so I hope it use less system resources. 3. Support keyboard shortcut, so you can use keyboard like an desktop calculator, press 'ALT' key will show them. 4. In standard calculator, it has a tip (15%) button, for example: you spent at a nice restaurant and you'd like to pay 15% tips, which is .75.