Systems, methods and computer program products create an equivalent circuit of electric andor electronic circuit components, by identifying groups of components and hierarchically modeling aggregate interactions among the groups of components, to create increasingly higher level circuit models, until the equivalent circuit for the components is produced. The tensioner further includes a collar portion, and is provided with a handle having a core portion on which the collar portion is disposed for axial movement, and a grip portion. The mobile device, also recieves signals from each of a plurality of reference devices at a corresponding known position when the mobile device is at each of the plurality of positions. The enhanced gripping means are provided by a toothed gripping means or a friction enhancing means. The safety needle is also provided with various finger gripping structures to facilitate manipulation of the safety needle device relative to the patient.