diff --git a/include/state_estimation/GroundLevelEstimator.h b/include/state_estimation/GroundLevelEstimator.h
new file mode 100644
index 0000000..2bae780
--- /dev/null
+++ b/include/state_estimation/GroundLevelEstimator.h
@@ -0,0 +1,55 @@
+#ifndef AGL_DETECTOR_H
+#define AGL_DETECTOR_H
+#include <cstdint>
+/*
+TWO RULES - 2 input functions, 1 output:
+
+input
+Update function: current ASL in meters as a DataPoint type
+Launch Dectcted: Call this when launch has happened (MUST BE SURE)
+
+output
+GetEGL (estimated ground level), returns a float that represents how many meters above sealevel the rocket was before launch
+*/
+
+class GroundLevelEstimator{
+    public:
+        /**
+         * @brief Constructs a GroundLevelEstimator.
+         */
+        GroundLevelEstimator();
+
+        /**
+         * @brief Updates the ground level estimate or converts ASL to AGL.
+         * 
+         * Before launch: Records altitude samples to estimate ground level.
+         * After launch: Converts the provided ASL altitude to AGL.             * 
+         * @param currentASL_m Current altitude above sea level in meters.
+         * @return Current altitude above ground level in meters.
+         */
+        float update(float currentASL_m);
+
+        /**
+         * @brief Signals that launch has been detected.
+         * 
+         * Stops recording ground level measurements and freezes the EGL.
+         * Should be called once when launch is confirmed.
+         */
+        void launchDeteched();
+
+        /**
+         * @brief Gets the estimated ground level.
+         * 
+         * @return Altitude above sea level at the launch site in meters.
+         */
+        float getEGL() const;
+
+    private:
+
+        bool launched = false; //Turned true if launch is detected
+        float estimatedGroundLevel_m = 0.0F; //EGL in meters
+        uint32_t sampleCount = 0; //Number of samples used for ground level estimate
+
+};
+
+#endif
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diff --git a/src/state_estimation/GroundLevelEstimator.cpp b/src/state_estimation/GroundLevelEstimator.cpp
new file mode 100644
index 0000000..31d5e0c
--- /dev/null
+++ b/src/state_estimation/GroundLevelEstimator.cpp
@@ -0,0 +1,34 @@
+#include "state_estimation/GroundLevelEstimator.h"
+
+// Constructor
+GroundLevelEstimator::GroundLevelEstimator()
+: launched(false), estimatedGroundLevel_m(0.0F), sampleCount(0)
+{}
+
+// Update the ground level estimate or convert ASL to AGL - Altitude ABOVE ground level
+float GroundLevelEstimator::update(float currentASL_m) {
+    
+    // Before launch: accumulate samples to estimate ground level
+    if (!launched) {
+        // Running average of ground level samples
+        estimatedGroundLevel_m = ((estimatedGroundLevel_m * sampleCount) + currentASL_m) / (sampleCount + 1);
+        sampleCount++;
+        
+        // Still on ground, so AGL is 0
+        return 0.0F;
+    }
+    
+    // After launch: convert ASL to AGL
+    return currentASL_m - estimatedGroundLevel_m;
+}
+
+// Signal that launch has been detected
+void GroundLevelEstimator::launchDeteched() {
+    launched = true;
+    // Ground level estimate is now frozen at estimatedGroundLevel_m
+}
+
+// Get the estimated ground level
+float GroundLevelEstimator::getEGL() const {
+    return estimatedGroundLevel_m;
+}
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