amplitude analog of (F-N) = 50 gammas. This is detected and recorded 

 to an accuracy of about ±3 gammas and scaled to an accuracy of 

 about ±1 gamma. Each base line, N, is established to an accuracy of 

 about ±20 gammas. Thus, the overall attainable accuracy of the VAM 

 intensity measurement is about ±25 gammas, or better. 



The VAM data are combined with Latitude, 0, and Longitude, X, to 

 obtain the following as tabular functions of time: 



Horizontal intensity = H = F cos I 

 Vertical intensity = Z = F sin I 

 Magnetic declination (variation) = D = TB - MH - RB + L 



where TB = True bearing of celestial body 



_1 sin (GHA - XW) 



— tan —— ^^- ~~~—~~~—~~ ~— ~ ~— ^ ——^— 

 cos (GHA - X W) sin - cos tan d 



and where GHA = Greenwich Hour Angle of celestial body 

 d = declination of celestial body 

 L = experimentally determined "lubber-line" 

 correction (a constant) 



From the above equations, and certain assumptions regarding the earth's 

 magnetic field, it is possible to estimate the error in each computed 

 magnetic element. Thus, the maximum probable error in H, AH, is 

 about ±100 gammas, and in Z, AZ, is about ±100 gammas. The maxi- 

 mum probable error in D, AD, is about ±0.25 degree, excluding errors 

 in TB due to uncertain (9 and X . 



The principal deficiency in the system described above lies in the 

 necessity for manual data tabulation, scaling, and reduction of data prior 

 to computation of the results. It is necessary to tabulate as functions of 

 time: MH, I, RB, F, (5 , X, GHA, and d, before the Computation Division 

 can reduce the data to punch cards for computation of H, Z, and D. 



The VAM system also allows for recording the aircraft heading with 

 respect to an Nl Compass System. This datum is useful for evaluating 

 auto- pilot performance, amount of turning in turbulent air, and so forth. 



Aircraft navigation and tracking are accomplished by standard naviga- 

 tional techniques that use the best available data for dead reckoning and 

 position fixing. Data sources include standard flight instruments, the 

 Nl Compass System (directional gyro), AN/APN-67 (Doppler radar 



Encl. (3) to Code 5401-BEO/bah memo of 23 Jul 1958 



B-ll 



