A screw compressor is equipped with a manually operated internal volume ratio adjusting slide valve and capacity adjusting slide valve. The wound wire comprises individual spirals that are twisted relative to each other, such that the individual spirals appear in a staggered formation, with the appearance of a chain section being varied by the number of spirals that are twisted at a particular time and the extent or angular dimension of the rotation imparted to such spirals. The emission spectra are correlated with the plasma charging voltage to identify the species contributing to the plasma charging voltage. When in use with a laptop, the first body and the second body unfold to an angle of 90 degrees relative to each other by means of the pivoting unit, so that the connector can be plugged with an electronic device.