@misc{indiciaec8e6450508b2,
  title = {Precision timekeeping using a small passive hydrogen maser},
  author = {Walls, F. L. and Howe, D. A.},
  year = {1981},
  url = {https://ntrs.nasa.gov/citations/19810018966},
  note = {Source identifier: 19810018966}
}