There are two comparison charts that focus solely on ACH Standard Entry Class (SEC) Codes that are used for consumer entries. This can be used as a great study tool if you're starting to become familiar with these SEC Codes. 

One chart highlights some of the important differences that exist between PPD Credits and Debits, WEB Credits and Debits, and TEL Entries. 

The second chart focuses on the Check Conversion entries and highlights the important differences that exist between POP, RCK, ARC, and BOC Entries.