20. Royalty paid on sound timber by the cubic foot
If any tree to be cut under any licence granted under these Rules, on which royalty is calculated according to its girth measurements, should prove to be unsound, the licensee shall work up all sound timber in such tree and shall pay royalty thereon by the cubic foot; and the Forest Ranger may stamp another tree of as nearly as possible the same size, and the licensee shall pay any increase of royalty which may thereby be incurred.