@misc{indiciae6c5bfc699b5a,
  title = {The geomagnetic secular variation 1900-1965},
  author = {Cain, J. C. and Hendricks, S. J.},
  year = {1968},
  url = {https://ntrs.nasa.gov/citations/19680012074},
  note = {Source identifier: 19680012074}
}