[greymule]

The Baseball Rules Differences is written and compiled by Carl Childress. It is "the only complete reference to all differences among National Federation, NCAA, NAIA, and Official [baseball] Rules." (Carl teaches English; note that he correctly uses among and not between.)

Carl revises and updates the BRD annually.

Even if you umpire only one of the codes, it's an extremely helpful book. For example, I couldn't find anything in the J/R or Evans about what the limits are on a retired runner who continues to run. But the BRD had a useful and informative section.

You can purchase the BRD from officiating.com