There are two very good introductory textbooks
on the subject by the same author:
http://faculty.luther.edu/~macdonal/laga/ http://faculty.luther.edu/~macdonal/vagc/index.html
http://faculty.luther.edu/~macdonal/laga/ http://faculty.luther.edu/~macdonal/vagc/index.html
This paragraph I think gives context to both the HN thread author and the commenter:
Geometric algebra as practiced today originated in the 1960’s. It is currently under vigorous development. It has found important applications in computer science (in graphics, robotics, and computer vision), engineering, and physics. It is available to game developers for the Xbox and PlayStation video game consoles. This text is an attempt to keep up with these modern developments.
Putting on my must read/study list (I am proficient in linear algebra, so hoping for a gentle push into geometric algebra)
Years ago (2009) I sent an e-mail to David Hestenes asking him if he was planning on writing an introductory textbook on geometric algebra. He said it was in the planning stages.
From what I understood later, it seems he is attempting to write a 100% purely geometric algebra book unlike macdonald who reserved it for the second part of laga.