def generate_diffs(hit):
    """ Takes a hit location and returns diffs like ONE_TWO: upper left to upper right """
    first_sensor = None
    for key in hit.keys():
        if hit[key] == 0:
            first_sensor = key
            break

    diffs = {
             "ONE_TWO" : (hit["one"] - hit["two"]),
             "ONE_THREE" : (hit["one"] - hit["three"]),
             "ONE_FOUR" : (hit["one"] - hit["four"]),
             "TWO_THREE" : (hit["two"] - hit["three"]),
             "TWO_FOUR" : (hit["two"] - hit["four"]),
             "THREE_FOUR" : (hit["three"] - hit["four"]),
             "first_sensor": first_sensor
             }
    return diffs