32 



HANDBOOK OF MAGNETIC COMPASS 



mentioned above by presenting the deviation values used in figure 21, 

 as plotted against magnetic headings as well as against compass 

 headings. 



Deviations on Compass Headings 



Deviations on Magnetic Headings 

 \ 



360 



HEADING - Degrees 



Figure 22. — Comparison of deviation curves. (Magnetic heading versus compass heading.) 



42. Napier's diagram, NBS 1103. — The Napier'^s diagram, figure 

 23, is a convenient scheme which permits a ready conversion of devi- 

 ations from compass to magnetic heading, or vice versa, with only 

 one plot of the deviation curve. Deviations are plotted on the di- 

 agonal lines as instructed on the diagram. The curve in figure 23 

 represents the same deviation values as in figure 21. Such a plot on 

 the Napier's form further reduces the calculations necessary for navi- 

 gation by graphically adding or subtracting the appropriate devia- 

 tion. However^ if the deviations are small, a Navier''s plot is of little 

 value. 



