A typical production layout consists of a sequence that advances re the limits of the ore body or property boundary and is then retreated. The advancing sequence (Figure 12.2) has an extraction ratio of about 40%. After these rooms are completed, the belt tailpiece and rigid frame structure is advanced 49 m (160 ft), and the sequence is repeated. Belt storage units are set in-line near the head of the panel belt to expedite moves. The retreat sequence (Figure 12.3) is characterized by a chevron pattern. The first belt move is a 24 m (80 ft) retreat. After the first retreat pattern is mined, subsequent moves of the retreating belt are on 49-m (160 ft) centers. The extraction ratio of the retreat pattern shown is also about 40%, resulting in an overall extraction of 80% The individual panel layouts are normally arranged side-by-side so that rooms driven perpendicular to the belt line will connect for purposes of ventilation.