One aspect of the invention provides a centrifugal compressor unit comprising a first motor, at least one compressor comprising a drive shaft driven by the rotor of the first motor and a set of impellers mounted on the drive shaft. An initial value of a potential difference VGS between a gate and a source of a switching transistor at the time of the verify is set to a value varied based on a resistance value level of multi-bit information. The first lever portion extends from the main body. The obturator is removably insertable in the first lumen through the open proximal end. Additional systems and methods are also presented.