An apparatus is used with a drilling assembly for drilling a borehole. The drilling assembly has an impact device linked to a drill head. The impact device is powered by a first fluid under a first pressure to impart a percussive force to the drill head. The percussive force is a function of the first pressure. A thruster of the drilling assembly is also linked to the drill head. The thruster is powered by a second fluid under a second pressure to impart a thrust force to the drill head. The thrust force is a function of the second pressure. Additionally, a rotator of the drilling assembly is linked to the drill head. The rotator is powered by a third fluid under a third pressure to impart a torque to the drill head. The torque is a function of the third pressure. The apparatus includes a first pressure sensor communicating with the first fluid to output a first electrical signal that is a function of the first pressure. A second pressure sensor communicates with the second fluid to output a second electrical signal that is a function of the second pressure. A third pressure sensor communicates with the third fluid to output a third electrical signal that is a function of the third pressure. A position sensor outputs a fourth electrical signal that is a function of depth of the drill head relative to a reference location. A device monitors the first, second, third and fourth signals. The device produces respective graph traces of functions of the percussive force, the thrust force, the torque and the depth.