A system for measuring a thickness of target material, comprising: a retrograde drill including a tubular shaft having a surface, a distal end, and a longitudinal axis, a drill bit disposed at the distal end of the tubular shaft , and at least one cutting member having a central axis , the cutting member being moveably disposed adjacent the distal end of the tubular shaft ; and a measurement tube , wherein the cutting member is operative to move between a first position where the central axis thereof is coincident with the longitudinal axis of the tubular shaft , and a second position where the central axis thereof is disposed at a non-zero angle relative to the longitudinal axis of the tubular shaft , the retrograde drill being operative to drill, in a retrograde fashion, at least one tunnel or bore through the target material with the cutting member of the retrograde drill disposed in the second position, wherein the tubular shaft of the retrograde drill has a plurality of linear graduation marks on the surface thereof for identifying a plurality of linear measures, respectively; characterised in that , the measurement tube is a substantially transparent measurement tube and has a proximal end and a distal end , the measurement tube being configured to receive and be slidingly engaged over the tubular shaft of the retrograde drill , wherein each of the plurality of linear graduation marks aligned with the proximal end of the measurement tube provides a respective linear measure of a distance between the distal end of the measurement tube and the cutting member of the retrograde drill disposed in the second position, the respective linear measure corresponding to the thickness of the target material remaining while drilling or after having drilled, in the retrograde fashion, the at least one tunnel or bore through the target material, and wherein at least some of the plurality of linear graduation marks are observable through the substantially transparent measurement tube . a retrograde drill including a tubular shaft having a surface, a distal end, and a longitudinal axis, a drill bit disposed at the distal end of the tubular shaft , and at least one cutting member having a central axis , the cutting member being moveably disposed adjacent the distal end of the tubular shaft ; and a measurement tube , wherein the cutting member is operative to move between a first position where the central axis thereof is coincident with the longitudinal axis of the tubular shaft , and a second position where the central axis thereof is disposed at a non-zero angle relative to the longitudinal axis of the tubular shaft , the retrograde drill being operative to drill, in a retrograde fashion, at least one tunnel or bore through the target material with the cutting member of the retrograde drill disposed in the second position, wherein the tubular shaft of the retrograde drill has a plurality of linear graduation marks on the surface thereof for identifying a plurality of linear measures, respectively; characterised in that , the measurement tube is a substantially transparent measurement tube and has a proximal end and a distal end , the measurement tube being configured to receive and be slidingly engaged over the tubular shaft of the retrograde drill , wherein each of the plurality of linear graduation marks aligned with the proximal end of the measurement tube provides a respective linear measure of a distance between the distal end of the measurement tube and the cutting member of the retrograde drill disposed in the second position, the respective linear measure corresponding to the thickness of the target material remaining while drilling or after having drilled, in the retrograde fashion, the at least one tunnel or bore through the target material, and wherein at least some of the plurality of linear graduation marks are observable through the substantially transparent measurement tube . <EOS>