A system for the treatment or diagnosis of tissue within a body, comprising: a medical device, comprising: an elongate, tubular shaft configured to be received within the body, said shaft having a proximal portion and a distal portion configured for movement relative to the proximal portion including by movement towards and away from the proximal portion along a longitudinal axis of said shaft and by deflection from the longitudinal axis; a flexible member disposed between the proximal and distal portions (68, 70) of said shaft, said flexible member having a predetermined stiffness; a first electromagnetic coil disposed within said shaft; and, a second electromagnetic coil disposed within said shaft and configured for movement with the distal portion of said shaft and relative to the first electromagnetic coil, said second electromagnetic coil connected in series with said first electromagnetic coil at a common node (84, 85); and, an electronic control unit configured to determine a specific contact force between the distal portion of said shaft and the tissue responsive to signals generated by one or more of said first and second electromagnetic coils, wherein said electronic control unit is further configured, in determining the specific contact force, to: generate a current in one of said first and second electromagnetic coils (44, 50); and, measure an electrical characteristic associated with the other of said first and second electromagnetic coils (44, 50), said electrical characteristic indicative of deformation of said flexible member and the specific contact force between the distal portion of said shaft and the tissue. a medical device, comprising: an elongate, tubular shaft configured to be received within the body, said shaft having a proximal portion and a distal portion configured for movement relative to the proximal portion including by movement towards and away from the proximal portion along a longitudinal axis of said shaft and by deflection from the longitudinal axis; a flexible member disposed between the proximal and distal portions (68, 70) of said shaft, said flexible member having a predetermined stiffness; a first electromagnetic coil disposed within said shaft; and, a second electromagnetic coil disposed within said shaft and configured for movement with the distal portion of said shaft and relative to the first electromagnetic coil, said second electromagnetic coil connected in series with said first electromagnetic coil at a common node (84, 85); and, an electronic control unit configured to determine a specific contact force between the distal portion of said shaft and the tissue responsive to signals generated by one or more of said first and second electromagnetic coils, wherein said electronic control unit is further configured, in determining the specific contact force, to: generate a current in one of said first and second electromagnetic coils (44, 50); and, measure an electrical characteristic associated with the other of said first and second electromagnetic coils (44, 50), said electrical characteristic indicative of deformation of said flexible member and the specific contact force between the distal portion of said shaft and the tissue. an elongate, tubular shaft configured to be received within the body, said shaft having a proximal portion and a distal portion configured for movement relative to the proximal portion including by movement towards and away from the proximal portion along a longitudinal axis of said shaft and by deflection from the longitudinal axis; a flexible member disposed between the proximal and distal portions (68, 70) of said shaft, said flexible member having a predetermined stiffness; a first electromagnetic coil disposed within said shaft; and, a second electromagnetic coil disposed within said shaft and configured for movement with the distal portion of said shaft and relative to the first electromagnetic coil, said second electromagnetic coil connected in series with said first electromagnetic coil at a common node (84, 85); and, an electronic control unit configured to determine a specific contact force between the distal portion of said shaft and the tissue responsive to signals generated by one or more of said first and second electromagnetic coils, wherein said electronic control unit is further configured, in determining the specific contact force, to: generate a current in one of said first and second electromagnetic coils (44, 50); and, measure an electrical characteristic associated with the other of said first and second electromagnetic coils (44, 50), said electrical characteristic indicative of deformation of said flexible member and the specific contact force between the distal portion of said shaft and the tissue. generate a current in one of said first and second electromagnetic coils (44, 50); and, measure an electrical characteristic associated with the other of said first and second electromagnetic coils (44, 50), said electrical characteristic indicative of deformation of said flexible member and the specific contact force between the distal portion of said shaft and the tissue.