grid_mode partitions the screen into a grid and displays each molecule in one grid location. Each molecule rotates, zooms, etc in that grid. A possibly very useful option for PyMOL. Each grid area is assigned a grid_slot number. This allows you to assign objects to certain grids; very helpful. This can be useful when comparing homologous structures and you want to view and rotate the aligned structures side by side. This is similar to a multiple split screen view of the proteins. You can write your coursework about it.
Hint: When using grid_mode with many molecules, it's sometimes good to align their centers of mass. This puts them all squarely in the middle of their grid element. The alignto command from cealign can do this for you.
Hint: If you don't want to align the molecules (it's not reall necessary for grid_mode) you can just center them on some coordinate. See COM.
Note: Currently (Mar 29, 2008), grid_mode is only available from source and not from the precompiled versions of PyMOL.
# turn on grid mode set grid_mode,1 # turn off grid mode set grid_mode,0