def humanize_speed(c_per_sec):
    """convert a speed in counts per second to counts per [s, min, h, d], choosing the smallest value greater zero.
    """
    scales = [60, 60, 24]
    units = ['c/s', 'c/min', 'c/h', 'c/d']
    speed = c_per_sec
    i = 0
    if speed > 0:
        while speed < 1 and i < len(scales):
            speed *= scales[i]
            i += 1
    return '{:.1f}{}'.format(speed, units[i])
