One recent development by Nvidia is SLI for laptops. Generally, gaming laptops are not considered "rigs" as the term can also refer to the physical size of the system. Modern gaming laptops can achieve respectable game performance, but never quite match desktops in a class to class comparison, and most do not feature upgradeable graphics cards. Due to the relatively small size that the hardware has to fit in, cooling the heat-intensive components is a major problem affecting the performance of such laptops, usually causing degraded value for money performance-wise. Attempts at using the same performance hardware as desktops usually end in a decreased clock frequency of graphics chips to reduce heat, causing the poor value for money. One can find many value recommendations across the World Wide Web on websites like "TechRadar" or "Tom's Hardware". The introduction of the Nvidia GTX 900M series of mobile GPUs in late 2014 represented a significant advancement from the previous 800M series, lessening the gap with desktop systems and making gaming laptops a more viable alternative to desktop PCs. A newer approach in the gaming PC industry is to create small form factor desktops that are more compact and easier to transport than a normal full-sized system. Pitch angle (particle motion)  The pitch angle of a charged particle is the angle between the particle's velocity vector and the local magnetic field. This is a common measurement and topic when studying the magnetosphere, magnetic mirrors, ciconic cusps and polywells. See Aurora and Ring current  It is customary to discuss the direction a particle is heading by its pitch angle. A pitch angle of 0 degrees is a particle whose parallel motion is perfectly along the local magnetic field. In the northern hemisphere this particle would be heading down toward the Earth (and the opposite in the southern hemisphere). A pitch angle of 90 degrees is a particle that is locally mirroring (see: Magnetosphere particle motion). The equatorial pitch angle of a particle is the pitch angle of the particle at the Earth's geomagnetic equator. This angle defines the loss cone of a particle. The loss cone is the set of angles where the particle will strike the atmosphere and no longer be trapped in the magnetosphere while particles with pitch angles outside the loss cone will mirror and continue to be trapped. Where formula_2 is the equatorial pitch angle of the particle, formula_3 is the equatorial magnetic field strength, and formula_4 is the maximum field strength. Notice that this is independent of charge, mass, or kinetic energy. This due to the invariance of the invariance of the magnetic moment formula_5.