Page 697 THE smooth sheet 757 



shoreline is slcetched in pencil by eye through the new points so that it corresponds to the original. 

 The shoreline at the new scale may then be transferred by one of the methods described in 7561. 

 This same method can, of course, be used to increase or decrease the scale in any proportion by the 

 use of proportional dividers. 



757. Verification of Transfer 



The transfer of all the topographic details must be verified by a person other than 

 the one doing the original work. A statement that this has been done shall be included 

 in the Descriptive Report, accompanying the statement giving the source of the topo- 

 graphic detail (see 8i2G). If the detail is to be inked in the field (see 792), the verifica- 

 tion should be made after the inldng. 



76. PLOTTING THE POSITIONS 



As explained in 332, there are at present various methods or combinations of methods 

 by which the hydrography is controlled, depending on the conditions under which the 

 operations are carried on. The most common of these are: (a) The three-point fix 

 method in which the position of the vessel is determined by measuring simultaneously 

 the two angles between thi-ee control stations (see 333); and (b) the Radio Acoustic 

 Ranging method in which distances from the vessel to two or more hydrophone stations, 

 whose positions are known, are obtained- by subaqueous means (see 612 and 681). 



In this section is given the general procedure for plotting all positions as well as 

 the detailed procedure for the above two methods. In addition the methods for plot- 

 ting astronomic positions and dead reckoning are described. The procedure for plot- 

 ting positions determined by special methods will be apparent from the description of 

 those methods (see 3323) . 



Prior to plotting the positions, and at least once a month during the progress of 

 the plotting, the protractor must be tested and the metal protractor adjusted, if 

 necessary (see 4533). 



The positions on sounding lines are usually plotted in the order in which they were 

 taken; that is, the smooth plotter begins with position 1 of "A" day and plots all of the 

 positions on the smooth sheet in the order in which the work was actually executed in 

 the field. This is not obligatory, of course, and in fact it may be preferable to plot the 

 positions in critical areas first, especially if plotting is done whUe field work is still in 

 progress, in order to give immediate evidence whether additional work is required in 

 the area. 



In plotting the positions, use should be made of the entries in the Sounding Records 

 at the beginning of each day's work, giving the approxunate latitude and longitude of 

 the first position. This is given to facilitate the plotter in locating quickly that portion 

 of the smooth sheet on which the position falls. Similar information is given at the 

 beginning of any line starting in a new area. 



In plotting the smooth sheet, a certain systematic procedure is necessary to permit 

 the smooth plotter to attain speed and still retain accuracy in his work. As the plotting 

 proceeds, he soon learns to sense where there is some deficiency in the recorded data. 

 It is imperative for best results that the person plotting the smooth sheet be familiar 

 with the methods by which the field work was done. If the plotter has not actually been 

 engaged in similar work, he should study the Hydrographic Manual so thoroughly that 

 all phases of the work will be clear to him, and as the plotting proceeds he will be able 

 to visualize the progress of the vessel during the work. 



