490 HYDROGRAPHICAL SURVEYING [chap. xxi. 



The use of large-size station pointers, combined with chords 

 where necessary, with checks for the distances, computed as 

 the plotting proceeds, will afford the readiest method. 



For a provisional bearing we shall be mainly dependent upon 

 carrying on that first obtained when determining the scale 

 (see Sections III. and IV.), until opportunity occurs for a more 

 reliable one to be obtained. 



SECTION XI. 



SIGNALLING THE PLOT IP UNABLE TO COMMUNICATE 

 BY BOAT WITH THE VESSELS ENGAGED. 



When desirous of communicating to other ships present the 

 result of any plot, time will be saved, should the weather be 

 unsuitable for communication by boat (when a tracing should 

 be sent), if this is done in the form of a concise signal, the angles 

 to the various objects being expressed as theodolite readings, 

 and distances expressed in inches. This data may be taken in 

 most cases with sufficient accuracy from the plot bj/ means of 

 rehable station pointers, whose errors are known, together with 

 beam compasses, selecting for this purpose any two extremes 

 of the triangulation as a common zero line, the bearing of which 

 should also be given. 



On this signal being repeated back correctl}^ it can be quickly 

 plotted on board the recei"vnng ships, the data given being suffi- 

 cient to check any doubt or evident mistake should it arise. 



Care, of course, is necessary in the first case, and the data 

 to be signalled should be checked independently before trans- 

 mission, a tracing of the plot being sent on the first opportunity 

 in confirmation of the signal. 



Specimen Signal. 



SignalUng the Plot (see Fig. IV.). 



Signal. 

 At " Had " Beacon. 

 Height 

 Wing 

 Plane 

 Vol .. 

 Sail . . 



