Some book recommendations here:
https://nebackgammon.org/index.php/r...es/nebc-books/
Elo rating system which FIBS and GridGammon uses, though I think GridGammon modifies it a bit for 1 and 2 point matches at least:
https://www.bkgm.com/faq/Ratings.html
Rating calculator for various sites:
http://www.columbusbg.org/Ratings/
Elo to error rate/PR discussion:
https://forumserver.twoplustwo.com/1...rates-1794369/