Page 707 the smooth sheet 7637 



d. Errors inherent in the R.A.R. method. — There are certain inherent errors in the R.A.R. method 

 of control of which little is known at present. One of these is that the time interval for an R.A.R. 

 distance from a nearby control station is apparently shorter than it should be. The cause of this 

 and the distance at which the effect ceases to exist are not definitely established, but it has been 

 detected in distances up to 7 or 8 seconds from a station. 



Another error, the cause of which is unknown, occurs on lines far distant from the control stations 

 where, with the same sized Vjomb, the time intervals apparently lengthen slightly more than they 

 should as the survey ship proceeds away from the stations. In such cases, if a change is made to a 

 larger bomb, the excess time distance is apparently reduced. And just the opposite effect is noted 

 when the ship is heading toward the control stations from far offshore. 



Since neither the cause nor the magnitude of these errors is known, there is no way of compensating 

 for them. Further experiments in the field may disclose a solution to these and other problems. 



e. Errors in hearings. — Bearings are only accurate where they are observed to comparatively close 

 objects. In general, those observed to an object not more than 4 miles away may be considered 

 reliable, but some of these and all of those taken at greater distances should be used with caution. 



7637. Accepting and Inking Positions 



After the analysis has disclosed which distance arcs and position data are reliable 

 and to be used, the exact fitting of the dead reckoning to them and the pricking of the 

 finally accepted positions should be accomplished. The dead-reckoning plot will 

 seldom fit all of the accepted position data exactly. As one position after another is 

 finally decided upon and pricked, it is necessary to shift the dead-reckoning plot small 

 amounts to adjust it to the successively accepted positions. 



As the positions are accepted on a given sounding line, the distance arcs shall be 

 inked or left in pencil according to the following rules: 



(1) All arcs that are 3 mm or more distant from the accepted position are temporarily questioned 

 and the reduction and plotting are rechecked. If no errors are found and the arcs are not used in deter- 

 mining the R.A.R. position, they are left in pencil on the smooth sheet and the values are marked 

 "R" in the Bomb Record to indicate that they have been rejected. 



(2) All arcs within 3 mm of the accepted position that did not influence the location of the position 

 are inked on the sheet but are marked with a question mark (?) in the Bomb Record. 



(3) All arcs, regardless of their distances from the accepted position, which have influenced the 

 location of the position are inked on the smooth sheet. 



After the accepted positions have been pricked on the smooth sheet they should 

 be inked and numbered (see 7681) and the distance arcs inked. 



For purposes of identification the distance arcs from each K.A.R. station should 

 be inked in a distinctive color. The preferable colors in the order listed are carmine, 

 brown, green, purple, and blue. Where there are more than five R.A.R. stations on 

 one sheet a repetition of colors is necessary. Confusion will be avoided from such dupli- 

 cation if a study is first made of the returns received from the various stations. The 

 assignment of colors should be made by one familiar with the actual field operations of 

 that particular survey. Distance arcs should be inked with an over-all length of 6 or 

 7 mm, interrupted at the position dot and leaving a space in which to pencil the sound- 

 ing. Arcs that do not pass through or too near the position may be inked as short 

 continuous lines. 



Bearing-s should be inked as fine black lines, as above, but slightly longer. 



After the positions on a sounding line have been inked, the area covered by the line 

 should be cleaned with a soft art gum eraser before connecting the positions. In this 

 the dead reckoning must be used as a guide for changes in course which occurred be- 

 tween positions. 



