The diode modules are available in six different sizes; 2, 4, 6, 8, 12, and 16 moa. The size of the dot is measured in minutes of angle (moa), with 1 minute of angle being equal to 1 inch @ 100 yards (approx.). Example; a 2 moa module will produce a dot that will cover 2 inches of your target @ 100 yards, a 6 moa module will cover 6 inches, and so on. When you reduce the target distance by half, you also reduce the minute of angle by half. Example; the 2 moa module will cover 1 inch @ 50 yards, the 6 moa module will cover 3 inches @ 50 yards, and so on.