Updated 3/21/2024
The instructions below will take you step by step through the process.
Before you begin, make sure you are logged into an account on your Mac that has Administrator privileges.
Install XQuartz-2.8.5.pkg. This is the X11 windows system for Mac, which is needed by Gnuplot.
Log out of your user session and log back in (or just reboot your computer). This will ensure that your DISPLAY variable is configured correctly for X11.
Download and unzip gnuplot-5.2.8.zip, and put the unzipped folder on your Desktop.
Open a Terminal window (available in the Utilities folder under Applications) and type the following commands, exactly as shown:
cd ~/Desktop/gnuplot-5.2.8 ./configure --with-readline=builtin make sudo make install (type in your password)
If you get the message "The make command requires the command line developer tools. Would you like to install the tools now?", go ahead and click Install. After the installation finishes, you should be able to type gnuplot in the Terminal window to start Gnuplot. As a quick test, start Gnuplot and then type the command plot x**2 at the gnuplot> prompt. To exit from Gnuplot, just type quit or exit.
You can now delete the gnuplot-5.2.8 folder and zip file from your Desktop, as well as the XQuartz-2.8.5.pkg installation file.
Download and run the installation program gp528-win64-mingw.exe (for 64-bit Windows) or gp526-win32-mingw_2.exe (for 32-bit Windows). This should install everything that you need.