Best Calculator Apps for iPhone

Archimedes Calculator

The Archimedes Calculator app is described as the graphing calculator of the 21st century. 

The app is free if you just need to use it to automatically solve equations, but if you upgrade to the premium option you get access to the Formula Library and Plotting. 

Upgrade to the premium version for $4.99 and you'll find a load of features that turns your phone into a powerful graphing calculator.