Song and fellow scientists recorded various people performing a set of 24 gestures aircraft carrier deck personnel use, including arm waving and folding, and hand movements. They built software that determined each person's elbow, wrist and hand positions, including whether palms were open and whether thumbs were up or down. They completed that portion of research last year. Then, the team had to classify all these gestures according to their meanings. But this is complicated, because deck signals are a complex ballet of movement — it's not like a seaman makes one motion and then stops for a beat before starting another. So the algorithm has to determine a gesture's meaning without a clear beginning, middle and end.