def cB_to_zipf(cB):
    """
    Convert a word frequency from centibels to the Zipf scale
    (see `zipf_to_freq`).

    The Zipf scale is related to centibels, the logarithmic unit that wordfreq
    uses internally, because the Zipf unit is simply the bel, with a different
    zero point. To convert centibels to Zipf, add 900 and divide by 100.
    """
    return (cB + 900) / 100