GY-271 HMC5883L 3-Axis Electronic Compass Module

This module measures magnetic field strength along three axes, which lets firmware calculate an absolute compass heading rather than relying on wheel-rotation counts or IMU drift to estimate direction over time. That absolute reference is exactly what a navigation-aware ground robot, a simple autonomous boat, or a handheld direction-finding gadget needs to hold a heading reliably over a long run, since compass readings don't accumulate error the way gyroscope-only direction estimates do. It is commonly paired with an accelerometer or full IMU in sensor-fusion navigation setups, where the compass anchors long-term heading while the IMU handles fast short-term motion, and the I2C interface keeps wiring simple alongside other sensors sharing the same bus.