Below is a description of computer program files, mentioned throughout this textbook, that may be obtained by the readers in two ways: (1) free of charge at the website prepared by Susan McLean of NGDC/NOAA (http://www.ngdc.noaa.gov/seg/potfld/geomag.shtml) or (2) on a high-density (1.4 Mb) floppy disk sold by NGDC/ NOAA.

At the website main page, select the highlighted “useful computer programs.” The executable files are designed for a DOS-compatible, personal computer. The programs were designed to assist the user in understanding the subject of geomagnetic fields; no claim is made regarding the suitability of the software for any other purpose. No restriction has been placed on the sharing of these programs; also, no warranty (expressed or implied), no endorsement, no guarantee of accuracy, and no responsibility for the program's functioning, can be made by the program authors, the author or publisher of this book, or by the National Geophysical Data Center. The files ending in. EXE are the executable programs; all the other files provide necessary input for some of the programs and must also be copied for proper operation of the set. If the files have been downloaded from the NGDC website, then copy all of them to a disk on your computer before running.

Geomagnetic Coordinates 1940–2005

The GMCORD program provides a determination of the geomagnetic coordinates for any selected global location. The program uses a polynomial fit (see the POLYFIT program below) of the dipole Gauss coefficients from the geomagnetic reference field models (see file ALL-IGRF.TAB below).