Bonus conversion, or PPB, is a statistic that describes a team's proficiency at earning points on bonuses. In formats where all bonuses are worth thirty possible points, bonus conversion is computed by dividing a team's total bonus points by the total number of bonuses heard, and is expressed in points per bonus (ppb). In formats where bonuses take different maximum point values over the course of the game, bonus conversion is computed by finding the average percentage of bonus points earned (total bonus points earned/total possible bonus points), and is expressed in percent per bonus (also ppb). For whatever reason, CBI uses the former definition even though their bonuses are not all worth the same amount of points.
Bonus conversion is used as a benchmark for tournament difficulty relative to attending teams. The standard for tournaments is that the best teams in the field should convert somewhere around 20 ppb, most teams should convert around 15 ppb, and the weak end of the field should convert somewhere around 10 ppb. Tournaments where many teams are converting over 20 ppb are considered too easy for the field; tournaments where many teams' ppb are in the single digits are considered too hard for the field.
Bonus conversion has been argued as the most fair way to break ties, as it is independent of opponent strength and roughly independent of possible variations in round-to-round question difficulty. When tiebreak packets are not available, most ACF and mACF tournaments follow convention and break ties based on bonus conversion.