https://thinking-forth.sourceforge.net/ https://thinking-forth.sourceforge.net/ <- A better source. The one you linked includes a number of typographical errors

https://thinking-forth.sourceforge.net/ https://thinking-forth.sourceforge.net/ <- A better source. The one you linked includes a number of typographical errors early on (OCR errors?) that were grating for me to try and read. None of the errors I noticed in your link were present in the copies I checked out here.