def cz2z(cz, e):
    """Transform from *z* index value to *z* index value, using the
    *e.css('cd')* (column depth) as column measure."""
    if cz is None:
        z = 0
    else:
        z = e.parent.pzf + cz * (e.css('cd', 0) + e.gd)
    return z
