The point on which a leveling rod is held between a foresight and the next backsight while the instrument is being moved to the next setup is called a TURNING POINT. It must be sufficiently stable to maintain the accuracy of the level line. Where either proper natural features of man-made construction is not available, a turning-point pin, a turning-point plate, or a wooden stake is used. These not only furnish the solid footings but also identify the same position for both sightings. Normally, the pins or plates are used for short periods and are taken up for future use as soon as the instrument readings are completed. Wooden stakes are used for longer periods except when wood is scarce or local regulations require their removal.

A turning-point pin is shown in figure 11-53, view A. It is made of a tapered steel spike with a round top with a chain or a ring through the shaft for ease in pulling. The pin is driven into the ground with a sledgehammer. After a turning pin has served its purpose atone point, it is pulled and carried to the next turning point. Turning-point plates (fig. 11-53, view B) are triangular metal plates with turned-down corners or added spikes that form prongs and have a projection or bump in the center to accept the rod. The plates are devised for use in loose, sandy, or unstable soils. The

plate is set by placing it on the ground, points down, and stepping on it to press it to a firm bearing. After use, it is lifted, shaken free of dirt and mud, and carried forward to the next turning point.