While we mostly used triangulation to delineate interesting rocks on our drawing, we found that the results worsened as we approached the edge of the trench, as the inaccuracies of the method became a high percentage of the measurement taken. Therefore, for the rocks around the centre of the trench, we decided to use offsetting and ‘swinging the tape’ in order to record these rocks.
Having pegged a tape horizontally along an edge of the trench, a second tape was used to measure horizontal displacement from this edge. In order to do this accurately, an angle of 90 degrees must be obtained between the two tapes. Rather than measure with a compass or optical square, we opted for the quicker method of holding the end of the tape firmly on the rock corner and then adjusting the tape so that it read the lowest reading possible, as the lowest reading would be obtained when there was a 90 degree angle between the rock-point and the baseline tape.