The Diamond System: How Carom Players Calculate Bank Shots

In three-cushion carom billiards, precision off the rail matters as much as touch on the cue ball. Most professional carom players rely on some version of the "diamond system" (also called the plus-two system) — a mathematical method that uses the diamond-shaped markers inlaid along the rails to predict exactly where a ball will travel after bouncing off one or more cushions.

How it works

Each rail carries evenly spaced diamond markers, typically eight per long rail and four per short rail. By assigning a numerical value to the cue ball's starting position and the target position, then applying a simple formula — subtracting the entry number from the exit number and adjusting by a fixed correction value depending on how many rails are involved — a player can calculate the aiming point on the first rail needed to send the ball toward the intended target.

Why it matters

Unlike pool, where balls are pocketed, three-cushion carom requires the cue ball to touch three cushions before contacting both object balls, leaving far less room for instinctive aiming alone. The diamond system gives players a repeatable, calculable reference point, especially valuable on long-rail combinations where visual judgment alone becomes unreliable.

Learning curve

Most instructors recommend players first master the basic "corner five" system — a simplified version that uses the number 5 as a reference constant — before progressing to variations that account for cue ball spin (english) and speed, both of which shift the rebound angle away from the mathematically "pure" path the diamond system predicts.

The system has been taught in carom billiards academies for generations and remains the foundation most world-class three-cushion players build their game around, even as spin and speed adjustments come from years of table feel rather than formula alone.