The Macintosh version of GDDCALC is a REALbasic application. Because of the way a REALbasic project is structured neither the code nor the window definitions are human-readable. If your wish is to modify or extend this version of GDDCALC you will need to install either the standard or professional version of REALbasic on your computer. (The standard version is quite inexpensive.) You will then be able to open and work with GDDCALC's project files, which contain all the code, window definitions, and images. The project files are contained here in a compressed tarfile. To access these files, place the compressed tarfile in a work directory, start the OSX Terminal utility in that directory, and issue the command
This will extract four files: gddcalc.rpb, about.gif, tutorial.gif, and
gleaves.jpg. You can then open gddcald.rbp with REALbasic.