EVGA GeForce GT 640
In UserPreferences -> System -> Compute Device, I have CUDA selected, and in the dropdown menu, GeForce GT 640 is selected, so Blender obviously knows my graphics card is there, and is supposed to be using it to render.
In the Properties -> Render panel, under the Device menu, I have “GPU Compute” selected.
Even though all these settings are correct, Blender always renders on CPU. I have a very large scene and I can’t afford to sit and wait 2 days for it to render on CPU