A rotary vacuum pump comprises, between the rotor and a driving motor, a control unit for operatively connecting the pump and the motor only in the periods in which the pump operation is required or desired. The method may have application to measurement of biological signals, in particular measurement of heart rate from a pulsatile blood signal. The spring carriage has a first section that fits into a gap space between the window frame and the window sash. The blade iron system also includes a blade iron having a motor mounting flange and a blade mounting portion. Redundancy generation includes implementations using non-systematic encoding, systematic encoding, or a hybrid combination. A visual electronic display is overlaid with the optical field of view.