sampling holes clearly extend further than the profile and production holes drilling the sampling holes naturally requires a longer time which fact the control system of the rock drilling apparatus takes into account when the drilling sequence is formed in addition the information obtained about the rock type by means of the sampling hole is also considered when the drilling sequence is updated furthermore when the rock to be excavated is fragmented rock the tunnel must be reinforced by rock bolts or the like consequently holes 21 in the transverse direction are drilled into the ceiling and walls of the tunnel drilling such bolt holes is also taken into account in the drilling sequence in fig4 a dashed line indicates the round 19 i e the portion that is loosened from the rock when an explosion is carried out as shown the rock material is not loosened along the bottom of the holes 13 15 wherefore the depth of the drilling holes has to be dimensioned so as to be somewhat longer than the planned length of the round when the following round is started to be drilled the new drilling holes have to be positioned somewhat differently in comparison with the previous drilling holes of the round for safety and drilling technical reasons if the operator decides to drill more holes during a drilling cycle for instance owing to the poor detachment properties of the rock or the damaged structure of the rock the control system observes the change made in the following updated control sequence fig5 shows a display unit 22 connected to the control unit a display 23 of which showing the operator of the rock drilling apparatus the.