9443 HYDROGRAPHIC MANUAL PaGE 866 



In converting these traverse values into minutes of arc and meters, using Special 

 Publication No. 5, use the metric value of 1 minute for the mid latitude of any traverse 

 distance to convert latitudes — hut the metric value of 1 minute of longitude for the 

 latitude of the terminal buoy must be used to convert longitudes — ^not only for the 

 terminal buoy itself but for each of the intermediate buoys. 



In this method of computation the time saved by not having to compute and check 

 the geographic positions, as in 9441, will probably more than compensate for the addi- 

 tional time needed to apply the required corrections. 



9443. Finding Location of Large Closure Error 



An accurate buoy traverse will generally close with an error of about 1 meter per 

 statute mile of traverse, and where the closure error is much larger than this, a blunder 

 may have been made in the computations. If there is a large error of closure, an analy- 

 sis of a graphic plot showing the error will often give a clue to its location. 



Buoy positions are almost always 

 plotted on the boat sheet as they are 

 computed, for use in controlling the 

 hydrography. Tliis constitutes a 

 graphic plot of the traverse in which 

 the relation between the fixed posi- 

 tion of the tie-in buoy and its position 

 as computed from the traverse may 

 be shown. Figure 186 illustrates a 

 graphic plot of a traverse starting at 



FIGURE 186.-TO locate a large closure error in a buoy traverse. buoy A and ending at BuOy E. 



The difference between the fixed 

 position of buoy E and its computed position is the closure error EE'. If the azimuth 

 of EE' is nearly the same as the azimuth of one of the lines of buoys, it is likely that the 

 closure error is due to an error in one of the distances used in computing that part of 

 the traverse. 



Where the azimuth of EE' approximates none of the azimuths of the lines of • 

 buoys, the following test may disclose the location of a gross error in the field work or a 

 blunder in the computations, causing an error in azimuth. A line is drawn joining E 

 and E' and a perpendicular bisector is drawn at the midpoint, as shown in the figure. 

 If it passes near a buoy position, an error in azimuth was probably made at that buoy. 

 In the case illustrated, the azimuth between buoys (7 and D should first be checked, and 

 reobserved if necessary, in attempting to find the error. 



95. FORMS AND PUBLICATIONS 

 951. List of Forms 



For convenient reference there are listed here the forms mentioned in the Hydro- 

 graphic Manual; the list includes practically all the forms that are commonly needed 

 in hydrographic surveying. Reference numbers given refer to those headings in the 

 text under which the use of a form is described in more or less detail; no reference 

 number is given opposite forms which are merely mentioned in the text. In request- 

 ing forms from the Office, all those listed whose numbers are not preceded by a letter 

 should be ordered on Form 11a, but the experimental forms listed (those whose niun- 

 bers are preceded by a letter) should be identified by both number and title. 



