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The length of the rocker handle is important—it should be waist-high to the operator in a standing position. The long leverage thus provided makes the rocker much easier to handle and materially reduces the physical effort which, at best, is considerable. Anyone who has attempted to operate a short-handled rocker from a sitting position will appreciate the foregoing comment.
Like panning, rocking relies to some degree on subtle techniques which must be learned by experience but the following pointers may help the novice get off to a good start. The first step is to set the bed plate and secure it so that it will not shift or move around when the rocker is in operation. The best slope for the rocker will have to be determined by trial but if it is initially set at 1 1/2 inches fall per foot of length, a few short trial runs will suffice to make any needed adjustment. Insufficient grade may cause sand to blanket the riffles and result in loss of fine gold. If the hopper is filled too full, gravel will slop over the sides when rocked and it will be difficult to regulate the flow of material through the screen and, for this reason, the hopper should not be filled over half full and preferably the screen plate should be left partially exposed at one end.
Starting at the exposed end of the screen plate, water is poured over the gravel while the rocker is shaken vigorously and the amount of material fed to the riffles is regulated by shifting the point of water application back and forth between the gravel and the exposed screen plate. Most pictures illustrating the use of a rocker show the water being applied with a long-handled dipper such as a gallon can on the end of a stick. In practice one finds that it takes considerable dexterity to use a dipper and at the same time operate the rocker smoothly and maintain a uniform flow of material over the riffles. For this reason, a water hose supplied by a pump or a gravity-flow should be provided where possible. The flow of water obtainable from an ordinary garden hose (about 5 gallons per minute) is usually enough for operating a rocker but where this is not available, two or three barrels of water used in a.closed circuit will generally be sufficient for a day's work. When water must be dipped, the water barrel should be placed next to the head-end of the rocker within easy reach of a short-handled dipper.
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