In x-ray crystallography why is it necessary to oscillate the crystal by a few degrees to get proper spot intensities?
An interesting question. The reason is due to the mosacity in the crystals, the Bragg peaks spread and so their intensity is not measured properly, usually 0.1 degree rotation is needed to get 'full' intensity. Without measuring full intensity it is really difficult to index the space group. And you need a lot of data and use Monte Carlo methods to make a best guess