Mercury - Rudder Angle Gauge White Face 2-1/8" (52 mm) 79-8M0052872. Overview. The Mercury Rudder Angle Gauge (79-8M0052872) helps you know exactly where your rudder is positioned - giving you better steering awareness and control, especially in tight docking situations or while maneuvering at slow speeds. It features a white face, black markings, and a glass lens for clear readability, and it fits a standard 2-1/8" (52 mm) dash opening. Designed for SmartCraft-capable systems, it provides real-