@misc{indiciae0c45df1ce3ca,
  title = {Improved ultrasonic standard reference blocks},
  author = {Eitzen, D. G. and Sushinsky, G. F. and Chwirut, D. J. and Bechtoldt, C. J. and Ruff, A. W.},
  year = {1976},
  url = {https://ntrs.nasa.gov/citations/19770006493},
  note = {Source identifier: 19770006493}
}