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20 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS Figure 31.-Sounding weight with compass and sonic transducer ready for cusembly. Standup cable cars have reel seats attached to the structural members of the car. (See fig. 35.) A sheave attached to the structural mem- bers carries the sounding line so that the sound- ing weight and current meter will clear the bottom of the car. Power reels can also be used on standup cable cars. Carrier cables are being used on deep, narrow streams for measuring as well as for sediment sampling. They are used in areas where it is impossible to wade, where no bridges are avail- able, and where it has been impractical to build a complete cableway. The assembly is operated from the shore. Bridljt: equipment When one measures from a bridge, the meter and sounding weight can be supported by a handline or by a sounding reel mounted on a crane or bridge board. The handline has been described on page 15. Two types of hand-operated portable cranes are the type A (see figs. 41, 42) for weights up to 100 pounds, and the type E for heavier weights. All cranes are designed so that the super- structure can be tilted forward over the bridge rail far enough for the meter and weight to clear most rails. Where bridge members are found along the bridge, the weight and meter can be brought up, and the superstructure can be tilted back to pass by the obstruction. (See fig. 41.) Cast-iron counterweights weighing 60 pounds each are used with four-wheel base cranes. (See fig. 42.) The number of such weights needed depends upon the size of sounding weight being supported, the depth and velocity of the stream, and the amount of debris being carried by the stream. A protractor is used on cranes to measure the angle the sounding line makes with the vertical when the weight and meter are dragged down- stream by the water. The protractor is a graduated circle clamped to an aluminum I ,