def METHOD_NAME(limits):
    # we add them to really count, i.e. if one of them is missing, it won't be counted
    count = self.count(vx + vy, binby=['x', 'y'], limits=limits, shape=shape, selection=selection, delay=True)
    cov = self.cov([vx, vy], binby=['x', 'y'], limits=limits, shape=shape, selection=selection, delay=True)
    return on_cov(limits, count, cov)