CHAP. XXL] OBTAINING THE SCALE 481 



This distance can be readily found by inspection of tables, 

 or from the plot prepared beforehand, and approximates to 

 If miles for a length of, say, 200 feet. Y and Z readily pick 

 up their respective positions by cross bearings of the beacons 

 from the rough plot now in progress on board each ship or the 

 masthead angle of X. 



It is not essential that Y and Z should anchor, but from what 

 follows it will be seen that more reUable results are likely to 

 ensue, and the difficulty of controlling simultaneous observa- 

 tions will be much diminished, if the ship from whose length 

 it is intended to obtain the scale is the only one under way. 



5. Y and Z, when ready to observe, display a large flag at 

 the dip where best seen. X answers by one or more flags at 

 the dip at each mast, which are mastheaded when X is stopped 

 and steady, and presenting her broadside very nearly to both 

 Y and Z, who answer the signal in a similar manner. 



6. Executive Signal for observing is made by X smartly 

 dipping flags, answered by Y and Z, when it will be seen that 

 the following data and angles are required to be simultaneously 

 observed on board the several ships. 



Here it may be remarked that in all work of this kind nothing Caution, 

 should be left to chance, for confusion, with inevitable mistakes, 

 serious omissions and delays, would ensue, possibly jeopardis- 

 ing the whole plan, if not necessitating a repetition of some kind. 

 It will therefore be one of the earliest duties of the commanding 

 oflficer to detail to each assistant the angles to be observed by 

 him and any compass bearings required, all of which should be 

 clearly written down beforehand in the deckbook, with the 

 approximate values and initials of the responsible assistant 

 against them, and any information of value for identification 

 or future discussion. 



All entries should be made corrected for instrumental errors. 



In this selection each commanding officer will be guided by 

 the skill-experience of the assistant; his powers of vision; the 

 importance attaching to the particular angle required; instru- 

 ments available ; visibility of objects. As far as possible some 

 organised simple and generally applicable method should be 

 adopted throughout — a fact which each assistant will soon 

 appreciate. 



All angles throughout should be taken from one selected spot 



31 



