We conduct patch tests on our multi-beams to detect any fine misalignment between the survey sensors, allowing us to produce a highly accurate and finely calibrated data set. Senior Surveyor Dave Mundy explains the method, which involves post process analysis of the multi beam data to determine angle offsets in the transducers and motion sensors. Dave shows how biases are determined using software that maps a series of lines over a distinct feature on the sea floor and demonstrates data with and without the biases applied.