Riffle—A manual sample divider that splits the coal
stream into two parts when it is directed through alternating
slots. Riffle slots shall be at least three times the top size of the
coal being divided and have an even number of alternating
slots, in order to achieve similar mass delivered to each catch
pan. Riffles shall be enclosed. The slope of the feed chutes and
riffles shall be at least 60°.