A scroll compressor (also known as a scroll vacuum pump) uses two interleaved spiral-like vanes to compress gases. The vane geometry may be involute, archimedean spiral, or hybrid curves. The scroll compressor concept was first developed in the early 1900s. A scroll is an involute spiral which, when matched with a mating spiral scroll form as shown in Figure 9, generates a series of crescent-shaped gas pockets between the two scroll elements. Scroll compressors work by moving one spiral element inside another stationary spiral to create a series of gas pockets that become smaller and increase the pressure of the gas. The largest openings are at the outside of the scroll where the gas enters. As these gas pockets are closed off by the moving spiral, the pockets move towards the center of the spirals and become smaller and smaller. This increases the pressure of the gas until it reaches the center of the spiral and is discharged through a port near the center of the scroll. The entire process is continuous. The moving scroll orbits in an eccentric path within the stationary (fixed) scroll as it creates the series of gas pockets. During compression, several pockets are being compressed simultaneously, resulting in a very smooth process. Maintaining an even number of gas pockets on opposite sides reduces any vibration inside the compressor.