21.   The Peterson system, as it has become known, spawned a series of highly useful guides that is still going strong.

22.   We have relied on those well-considered Notes as a useful guide in ascertaining the meaning of the Rules.

23.   Word of mouth and gut feelings are both useful guides, but most of us want something more solid to rely on.

24.   Yet, if that track employee is on top of the game, the morning line printed in a racing program can be a useful guide for fans.

25.   The weights serves as a useful guide to racegoers on the local circuit, which are announced before the start of the race.