Geometrical optics treats all light as rays, to estimate light path, imaging, and optical properties such as aberration and light distribution. Geometrical optics is used when typical dimensions are much larger than the wavelength light. In applications such as waveguides that are on the order of wavelength, treatment of light as waves, rather than rays, is more appropriate, and requires calculations that involve wave equations. Ray tracing is simply performed by following the refraction and reflection principles. Basically the laws of refraction governed by Snell's law are simply applied at every interface. After establishing ray tracing, the next step is to measure other characteristics, such as aberrations, which is a measure of how well an optical system has the ability to image an object. The graphical method of ray tracing involves following the light path graphically, using laws such as reflection, refraction, or thin lens formulation.