diff --git a/include/input/MotionPredictorMetricsManager.h b/include/input/MotionPredictorMetricsManager.h
index 6284f07..12e50ba 100644
--- a/include/input/MotionPredictorMetricsManager.h
+++ b/include/input/MotionPredictorMetricsManager.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2023 The Android Open Source Project
+ * Copyright 2023 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -14,23 +14,193 @@
  * limitations under the License.
  */
 
-#include <utils/Timers.h>
+#include <cstddef>
+#include <cstdint>
+#include <functional>
+#include <limits>
+#include <optional>
+#include <vector>
+
+#include <input/Input.h> // for MotionEvent
+#include <input/RingBuffer.h>
+#include <utils/Timers.h> // for nsecs_t
+
+#include "Eigen/Core"
 
 namespace android {
 
 /**
  * Class to handle computing and reporting metrics for MotionPredictor.
  *
- * Currently an empty implementation, containing only the API.
+ * The public API provides two methods: `onRecord` and `onPredict`, which expect to receive the
+ * MotionEvents from the corresponding methods in MotionPredictor.
+ *
+ * This class stores AggregatedStrokeMetrics, updating them as new MotionEvents are passed in. When
+ * onRecord receives an UP or CANCEL event, this indicates the end of the stroke, and the final
+ * AtomFields are computed and reported to the stats library.
+ *
+ * If mMockLoggedAtomFields is set, the batch of AtomFields that are reported to the stats library
+ * for one stroke are also stored in mMockLoggedAtomFields at the time they're reported.
  */
 class MotionPredictorMetricsManager {
 public:
     // Note: the MetricsManager assumes that the input interval equals the prediction interval.
-    MotionPredictorMetricsManager(nsecs_t /*predictionInterval*/, size_t /*maxNumPredictions*/) {}
+    MotionPredictorMetricsManager(nsecs_t predictionInterval, size_t maxNumPredictions);
 
-    void onRecord(const MotionEvent& /*inputEvent*/) {}
+    // This method should be called once for each call to MotionPredictor::record, receiving the
+    // forwarded MotionEvent argument.
+    void onRecord(const MotionEvent& inputEvent);
 
-    void onPredict(const MotionEvent& /*predictionEvent*/) {}
+    // This method should be called once for each call to MotionPredictor::predict, receiving the
+    // MotionEvent that will be returned by MotionPredictor::predict.
+    void onPredict(const MotionEvent& predictionEvent);
+
+    // Simple structs to hold relevant touch input information. Public so they can be used in tests.
+
+    struct TouchPoint {
+        Eigen::Vector2f position; // (y, x) in pixels
+        float pressure;
+    };
+
+    struct GroundTruthPoint : TouchPoint {
+        nsecs_t timestamp;
+    };
+
+    struct PredictionPoint : TouchPoint {
+        // The timestamp of the last ground truth point when the prediction was made.
+        nsecs_t originTimestamp;
+
+        nsecs_t targetTimestamp;
+
+        // Order by targetTimestamp when sorting.
+        bool operator<(const PredictionPoint& other) const {
+            return this->targetTimestamp < other.targetTimestamp;
+        }
+    };
+
+    // Metrics aggregated so far for the current stroke. These are not the final fields to be
+    // reported in the atom (see AtomFields below), but rather an intermediate representation of the
+    // data that can be conveniently aggregated and from which the atom fields can be derived later.
+    //
+    // Displacement units are in pixels.
+    //
+    // "Along-trajectory error" is the dot product of the prediction error with the unit vector
+    // pointing towards the ground truth point whose timestamp corresponds to the prediction
+    // target timestamp, originating from the preceding ground truth point.
+    //
+    // "Off-trajectory error" is the component of the prediction error orthogonal to the
+    // "along-trajectory" unit vector described above.
+    //
+    // "High-velocity" errors are errors that are only accumulated when the velocity between the
+    // most recent two input events exceeds a certain threshold.
+    //
+    // "Scale-invariant errors" are the errors produced when the path length of the stroke is
+    // scaled to 1. (In other words, the error distances are normalized by the path length.)
+    struct AggregatedStrokeMetrics {
+        // General errors
+        float alongTrajectoryErrorSum = 0;
+        float alongTrajectorySumSquaredErrors = 0;
+        float offTrajectorySumSquaredErrors = 0;
+        float pressureSumSquaredErrors = 0;
+        size_t generalErrorsCount = 0;
+
+        // High-velocity errors
+        float highVelocityAlongTrajectorySse = 0;
+        float highVelocityOffTrajectorySse = 0;
+        size_t highVelocityErrorsCount = 0;
+
+        // Scale-invariant errors
+        float scaleInvariantAlongTrajectorySse = 0;
+        float scaleInvariantOffTrajectorySse = 0;
+        size_t scaleInvariantErrorsCount = 0;
+    };
+
+    // In order to explicitly indicate "no relevant data" for a metric, we report this
+    // large-magnitude negative sentinel value. (Most metrics are non-negative, so this value is
+    // completely unobtainable. For along-trajectory error mean, which can be negative, the
+    // magnitude makes it unobtainable in practice.)
+    static const int NO_DATA_SENTINEL = std::numeric_limits<int32_t>::min();
+
+    // Final metrics reported in the atom.
+    struct AtomFields {
+        int deltaTimeBucketMilliseconds = 0;
+
+        // General errors
+        int alongTrajectoryErrorMeanMillipixels = NO_DATA_SENTINEL;
+        int alongTrajectoryErrorStdMillipixels = NO_DATA_SENTINEL;
+        int offTrajectoryRmseMillipixels = NO_DATA_SENTINEL;
+        int pressureRmseMilliunits = NO_DATA_SENTINEL;
+
+        // High-velocity errors
+        int highVelocityAlongTrajectoryRmse = NO_DATA_SENTINEL; // millipixels
+        int highVelocityOffTrajectoryRmse = NO_DATA_SENTINEL;   // millipixels
+
+        // Scale-invariant errors
+        int scaleInvariantAlongTrajectoryRmse = NO_DATA_SENTINEL; // millipixels
+        int scaleInvariantOffTrajectoryRmse = NO_DATA_SENTINEL;   // millipixels
+    };
+
+    // Allow tests to pass in a mock AtomFields pointer.
+    //
+    // When metrics are reported to the stats library on stroke end, they will also be written to
+    // mockLoggedAtomFields, overwriting existing data. The size of mockLoggedAtomFields will equal
+    // the number of calls to stats_write for that stroke.
+    void setMockLoggedAtomFields(std::vector<AtomFields>* mockLoggedAtomFields) {
+        mMockLoggedAtomFields = mockLoggedAtomFields;
+    }
+
+private:
+    // The interval between consecutive predictions' target timestamps. We assume that the input
+    // interval also equals this value.
+    const nsecs_t mPredictionInterval;
+
+    // The maximum number of input frames into the future the model can predict.
+    // Used to perform time-bucketing of metrics.
+    const size_t mMaxNumPredictions;
+
+    // History of mMaxNumPredictions + 1 ground truth points, used to compute scale-invariant
+    // error. (Also, the last two points are used to compute the ground truth trajectory.)
+    RingBuffer<GroundTruthPoint> mRecentGroundTruthPoints;
+
+    // Predictions having a targetTimestamp after the most recent ground truth point's timestamp.
+    // Invariant: sorted in ascending order of targetTimestamp.
+    std::vector<PredictionPoint> mRecentPredictions;
+
+    // Containers for the intermediate representation of stroke metrics and the final atom fields.
+    // These are indexed by the number of input frames into the future being predicted minus one,
+    // and always have size mMaxNumPredictions.
+    std::vector<AggregatedStrokeMetrics> mAggregatedMetrics;
+    std::vector<AtomFields> mAtomFields;
+
+    // Non-owning pointer to the location of mock AtomFields. If present, will be filled with the
+    // values reported to stats_write on each batch of reported metrics.
+    //
+    // This pointer must remain valid as long as the MotionPredictorMetricsManager exists.
+    std::vector<AtomFields>* mMockLoggedAtomFields = nullptr;
+
+    // Helper methods for the implementation of onRecord and onPredict.
+
+    // Clears stored ground truth and prediction points, as well as all stored metrics for the
+    // current stroke.
+    void clearStrokeData();
+
+    // Adds the new ground truth point to mRecentGroundTruths, removes outdated predictions from
+    // mRecentPredictions, and updates the aggregated metrics to include the recent predictions that
+    // fuzzily match with the new ground truth point.
+    void incorporateNewGroundTruth(const GroundTruthPoint& groundTruthPoint);
+
+    // Given a new prediction with targetTimestamp matching the latest ground truth point's
+    // timestamp, computes the corresponding metrics and updates mAggregatedMetrics.
+    void updateAggregatedMetrics(const PredictionPoint& predictionPoint);
+
+    // Computes the atom fields to mAtomFields from the values in mAggregatedMetrics.
+    void computeAtomFields();
+
+    // Reports the metrics given by the current data in mAtomFields:
+    //  • If on an Android device, reports the metrics to stats_write.
+    //  • If mMockLoggedAtomFields is present, it will be overwritten with logged metrics, with one
+    //    AtomFields element per call to stats_write.
+    void reportMetrics();
 };
 
 } // namespace android