There are some differences between the calculator that the GRE will actually provide you and the one provided by TPR for your online tests. Notably, the TPR calculator lacks parenthesis, memory, and a square root operator while offering more precision than the eight digits of the actual GRE calculator. I am working on an iPhone application to more closely mimic the GRE calculator. If you would like to help test this, please send me your phone's UDID. This Ad Hoc Helper application makes finding and sending the UDID easy.
The Official GRE Calculator
The Princeton Review's GRE Calculator
