[COMMENT DELETED]

The ratings are based on how fast you solve them. There is a bar that decreases in percentage as the seconds tick away

some problems have two or three moves to solve

the level of difficulty is also based on your performance, the more you solve, the higher the difficulty

as for the mathematical calculations here, I am not sure if it is on the glicko system

maybe the community can answer that

You can try other puzzle sites, or sites dedicated to puzzles based on game history, but I am not sure if chess.com would permit me to list the sites on a public forum

and there are pdfs out there, and these are on public domain, so they are available for download at no cost, these are at chessville,

http://www.chessville.com/downloads/ebooks.htm

Thank you very much your help is very much appreciated, N