Abstract: The apparatus comprises two coaxial elements (1,2), a first element (4) provided between the said two elements (1,2) and arranged to combine them and to oppose the relative displacements of the elements along their common axis (3), when a stress along the axis is applied at the free end of one of these elements and directed towards the other element, and also to oppose the relative rotation of the elements, a probe (7) affixed to the free end (6) of one of the elements (2), a second element (8) provided at the free end (5) of the other element (1) to apply the aforementioned stress and a torque to the elements (1,2), a cursor (9) arranged to move along the element (2) bearing the probe (7), parallel to the axis (3), from the free end (10) of the probe (7) towards the other element (1), when the probe penetrates into the body or medium to be measured and a third element (11 ) arranged, in a first position, to enable the aforementioned stress along the axis (3) and the displacement of the cursor (7) on the elem