Fusion Calculator Lite is a simple and useful calculator!
You can put aside the numbers you calculated anywhere on the screen, simply by dragging them using your finger.
You can bring those numbers back again to add, subtract, multiply, or divide by another number you calculated.

Also, when you want to add-up all the numbers you have on the screen in one-touch, just push the green button on the upper-right corner.

This Free Version includes advertisement, so if you want a version without the ads, search for "Fusion Calculator" on the App Store. iPad version is also available!