To cite package ‘constants’ in publications use:

  Ucar I (2024). _constants: Reference on Constants, Units and
  Uncertainty_. R package version 1.0.1,
  <https://github.com/r-quantities/constants>.

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {constants: Reference on Constants, Units and Uncertainty},
    author = {Iñaki Ucar},
    year = {2024},
    note = {R package version 1.0.1},
    url = {https://github.com/r-quantities/constants},
  }