AIDS TO NAVIGATIOlSr 87 



The determination and establishment of the most satisfactory rates is normally the result 

 of coordination with the U.S. Coast Guard, and the decision of the Chief of Division. These 

 factors are important for consideration : 



1. The geographic distance of the stations of a given rate from the neatline limits of the 



chart. 



2. The relationship of rates to one another. The most satisfactory fixes are obtained where 



the intersections of the lines of position are normal to one another; the least satis- 

 factory are at or near baseline extensions. 



3. The existence of extensive shoal areas on a chart would preclude the overprinting of 



loran lines within these areas. 



On a printed copy of the chart the cartographer shall sketch in the desired lines of position, 

 preferably in the colors in which they are to be printed. Normally, a given rate is printed in 

 the same color on all charts ; any deviation from this shall be authorized only by the Chief of 

 Division. The lines of position shall be spaced approximately three-fourths of an inch apart 

 where convergence is greatest; as the lines of position diverge, intermediate lines shall be added. 

 Excepting near base-line extensions, no space shall be greater than the largest spacing of the 

 linear interpolator. Normally, every line of position is labeled; the 100-microsecond lines shall 

 carry the complete designation, as 2L4-1500, while intermediate lines may be designated only 

 as 1420, 1440, etc. The designation shall be kept aligned as far as possible, and are spaced 

 along each line at 15- to 18-inch intervals. 



A blueline made from the black negatives of the chart shaU be procured. The blueline 

 should be printed near the center of a large sheet of polyester plastic, on the grained side ; the 

 plastic shaU not be trimmed from the edges. 



Three principal forms of plotting data for loran lines of position are available: 



1. The bound copies of "Loran Tables", N.0.0. Publication No. 221 with specific sub- 



nimibers in parentheses. 



2. "Tab Runs", which are preliminary tables also obtained under limited distribution 



from the Oceanographic Office. 



3. Supplemental "tab runs" obtained from our own Computing Division to augment 



either of the above. 



A quick examination of the tables and tab runs above will show that intercept values 

 are provided for every 15' of arc at and near both stations where the hyperbolas change direc- 

 tion most rapidly. Further out from the two stations, intercepts are provided for every 30', 

 while at the greatest distances they are at every minute of arc. Rule in the necessary additional 

 projection lines in a non-photographic blue ink. The projection hues should be ruled outside 

 the neat lines as necessary to insure at least one plotted point for every line of position either, 

 on or outside the next lines. 



