To use the functions external/IDL_GEOPACK you will need to install Haje Korth's IDL wrapper for N.A. Tsyganenko's magnetic fields model package. To do this you must: #1 Download the IDL geopack for your architecture from: http://ampere.jhuapl.edu/code/idl_geopack.html or from the themis site: http://themis.ssl.berkeley.edu/software.shtml #2 Unzip the package to any directory #3 Copy the binary and the dlm file from the package you just unzipped into your idl dlm directory. Note: This may require assistance from your system administrator, if your IDL installation is centrally managed. The dlm file will be named: idl_geopack.dlm The binary will be named: idl_geopack.{extension} {extension} will vary from OS to OS on windows it will be called: idl_geopack.dll on linux and unix it will be called: idl_geopack.so Your idl dlm directory will vary depending on where you installed IDL but it can be found by typing: print,!DLM_PATH in an IDL terminal It is preferable to install the DLM files under the IDL installation directory, but if that is not possible, there is a workaround. On startup, IDL reads an environment variable called "IDL_DLM_PATH", and uses the directories specified there to locate DLM files, similar to how the IDL_PATH variable determines where to look for .pro files. So if IDL_DLM_PATH is set to "/home/jwl/my_dlm_files:", IDL will look for DLM files in /home/jwl/my_dlm_files first, then the IDL installation directories. Windows users can use the control panel to edit the environment variables to add an appropriate value for IDL_DLM_PATH. Linux, MacOs, and Solaris users can put the appropriate "setenv" command in their startup files. #4 after the files are copied just restart your idl session and idl should automatically detect the geopack functions. The boolean function igp_test() in the external/IDL_GEOPACK tests to be sure the package is in place. Typing print,igp_test() will check that it is installed correctly or you can type: geopack_help in IDL to test as well.