Harrison has one critical piece of information that you do not. Without it, you cannot determine the distance to the well with certainty. The information is not a measurement—Harrison will have no trouble determining it.
The critical piece of information that Harrison has is the location of the well.
To determine the distance to the well with certainty, you will need to obtain the critical piece of information from Harrison. It is essential to ask him for the information he has that can help in calculating the distance accurately. Without this additional information, it will not be possible to determine the distance with certainty.
