The engine of the RX-9 and AX-2 is the HBX Gen 4 Cam System. As the name implies, this is the 4th iteration of Hoyt's popular HBX cam system. Along with many other design improvements, the HBX cam system has changed the game when it comes to smooth draw, silent shots, and overall performance of our bows over the past few years. Hoyt designed modules to optimize performance for every inch of draw length range. Module 1 is the shortest inch of draw length. The module covers 1 inch in draw length range. For example, the number 5 module on the RX-9 maxes out at 30 inches and adjusts down to 29.25. The number 4 module will pick up at 29 inches and adjust down to 28.25, and so on.