The base line values, which are manually tabulated, are established 

 to an accuracy of about ±20 gammas. The base line accuracy is largely 

 dependent upon the stability of a group of mercury cells and standard 

 cells used as a voltage reference. 



The VAM utilizes a synchro system wherein a synchro control 

 transmitter is geared to the inductor- orienting device (or sextant 

 mount, in the case of RB)„ The transmitter is connected to a remote 

 synchro control transformer which is manually indexed to integer 

 5° base values (within 5° of the unknown angle). The transformer 

 a.c. output voltage, an amplitude analog of the difference between the 

 unknown and base values, is detected and recorded on two Esterline- 

 Angus recorders to give both a direct (instantaneous) value and a value 

 integrated over 100- second time intervals. The overall accuracy 

 exclusive of navigational and vertical reference errors is about 

 ±0.12 degree or better for each angle. 



The VAM vertical reference is provided by suspending the detecting 

 mechanism as a viscous- damped pendulum gimballed about the pitch 

 and roll axes of the aircraft. The gimbal mechanism and detector are 

 supported on a shock-mounted base. Ideally, in level flight the average 

 acceleration acting on the pendulum is the combination of gravity 

 and the Coriolis force. The deflection caused by the Coriolis force 

 is compensated by a manual adjustment. The angular data are inte- 

 grated for 100 seconds to achieve values with respect to a reasonably 

 good average vertical reference. However, this reference is affected 

 by aircraft accelerations and turbulence. 



2. Nuclear Precession Magnetometer 



The Varian V-4910 magnetometer measures total magnetic 

 intensity only. The instrument is absolute and nearly drift- free. 

 The principle of operation is based upon the gyromagnetic character- 

 istics of protons which can be made to precess like tiny spinning tops 

 at a frequency proportional to the magnetic field. However, the V-4910 

 has not yet been installed for airborne survey use. 



The data, digital rather than analog, will be punched periodically 

 on a paper tape as a twelve-digit binary number. The output also is 

 converted to an analog form and displayed on a Sanborn recorder. 



It is expected that the detector will be towed in an aerodynamic 

 "bird 11 developed by the Naval Air Development Center, Johnsville, 

 Pennsylvania, or possibly in a °drogue-like n device. 



XIV- 5 



