A low pass filter includes a first amplifier stage and a second amplifier stage. A blur module may render physically-realistic, spatially-varying blurs in digital images while at the same time giving users the flexibility to produce creative blur effects. The second arm also has a first end pivotally attached to the vehicle, and a second end pivotally attached to the stepping member. The operation control unit is arranged to allow operation of the propulsion device if authentication by the second authentication unit does succeed, and prohibit operation of the propulsion device if the authentication by the second authentication unit does not succeed. The interface module is configurable to be placed either in the control room or in the scan room. The housing further has an elastomeric element positioned along the top rim for gripping a user’s finger once inserted.