Ififi 



168 



NAUTICAL CHART MANUAL 



MAP SCALES AND EQUIVALENTS 



At 



Scale 



2,500 



5,000 



10,000 



15,000 



20,000 



30,000 



40,000 



50,000 



60,000 



80,000 



100,000 



200,000 



400,000 



500,000 



1,000,000 



1,200,000 



A nautical mile is a minute of an average great circle of the 

 earth, and its length is 6,076.11 feet, or 1,852.0 meters. A statute 

 mile is 5,280 feet, or 1,609.3 meters. One meter equals 39.37 

 inches; 1 centimeter equals 0.3937 inch; 1 inch equals 2.54 

 centimeters. 



LOGARITHMIC SPEED SCALE 



5 6 7 8 9 10 



.I..Jn„l,J I i I h I I i . . . 



15 



20 



25 



30 



40 



50 (50 



I ,,,,I,,,,Lm,I,,,,I.,J,,J,,:J 



To find SPEED, place one point of dividers on nautical miles run and the other on minutes run. Without changing divider spread, place 

 right point on 60 and left point will then indicate speed in knots. Example: with 4.0 miles run in 15 minutes, the speed is 16.0 knots. 



Distance of Visibility of Objects at Sea 



The following table gives the approximate geographic range of visibility for an object which may 

 be seen by an observer whose eye is at sea level ; in practice, therefore, it is necessary to add to these 

 a distance of visibility corresponding to the height of the observer's eye above sea level. 



FIGURE 37— Tables 



