52 



HYDROGRAPHIC MANUAL 



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FiGURK 10. — Three-arm plastic protractors. 



raphy is controlled by electronic devices 

 which measure distances to fixed stations, 

 positions are plotted by an Odessey Protrac- 

 tor (Fig. 12) with reference to distance cir- 

 cles drawn on the sheet (see 5-50). This 

 device is simply a series of closely-spaced 

 concentric circles drawn on clear plastic ma- 

 terial to represent distances from the center 



in terms of miles, microseconds, or lanes, to 

 fit the system in use. A protractor must be 

 constructed to suit the type of electronic 

 equipment to be used and the scale at which 

 the survey is to be plotted. The diameter 

 of the outer circle on the protractor is dou- 

 ble the interval between distance circles on 

 the sheet. 



