Al-Akhaly إ. ع. . “The International Geomagnetic Reference Field in Yemen at the Beginning of 2020 and The Secular Variations During the Period from 1900 to 2020”. Journal of Pure & Applied Sciences, vol. 20, no. 1, May 2021, pp. 153-66, doi:10.51984/jopas.v20i1.1181.