diff --git a/src/xrt/tracking/hand/mercury/hg_debug_instrumentation.hpp b/src/xrt/tracking/hand/mercury/hg_debug_instrumentation.hpp
new file mode 100644
index 000000000..a4974a9cb
--- /dev/null
+++ b/src/xrt/tracking/hand/mercury/hg_debug_instrumentation.hpp
@@ -0,0 +1,55 @@
+// Copyright 2023, Collabora, Ltd.
+// SPDX-License-Identifier: BSL-1.0
+/*!
+ * @file
+ * @brief  Debug instrumentation for mercury_train or others to control hand tracking.
+ * @author Moses Turner <moses@collabora.com>
+ * @ingroup tracking
+ */
+
+#pragma once
+
+#include "hg_interface.h"
+
+#include "util/u_var.h"
+
+
+#ifdef __cplusplus
+namespace xrt::tracking::hand::mercury {
+extern "C" {
+#endif
+
+struct hg_tuneable_values
+{
+	bool new_user_event = false;
+	struct u_var_draggable_f32 after_detection_fac;
+	struct u_var_draggable_f32 dyn_radii_fac;
+	struct u_var_draggable_f32 dyn_joint_y_angle_error;
+	struct u_var_draggable_f32 amount_to_lerp_prediction;
+	struct u_var_draggable_f32 amt_use_depth;
+	struct u_var_draggable_f32 mpiou_any;
+	struct u_var_draggable_f32 mpiou_single_detection;
+	struct u_var_draggable_f32 mpiou_double_detection;
+	struct u_var_draggable_f32 max_reprojection_error;
+	struct u_var_draggable_f32 opt_smooth_factor;
+	struct u_var_draggable_f32 max_hand_dist;
+	bool scribble_predictions_into_next_frame = false;
+	bool scribble_keypoint_model_outputs = false;
+	bool scribble_optimizer_outputs = true;
+	bool always_run_detection_model = false;
+	bool optimize_hand_size = true;
+	int max_num_outside_view = 6;
+	bool enable_pose_predicted_input = true;
+	bool enable_framerate_based_smoothing = false;
+
+	// Stuff that's only really useful for dataset playback:
+	bool detection_model_in_both_views = false;
+};
+
+struct hg_tuneable_values *
+t_hand_tracking_sync_mercury_get_tuneable_values_pointer(struct t_hand_tracking_sync *ht_sync);
+
+#ifdef __cplusplus
+}
+} // namespace xrt::tracking::hand::mercury
+#endif
diff --git a/src/xrt/tracking/hand/mercury/hg_sync.hpp b/src/xrt/tracking/hand/mercury/hg_sync.hpp
index d3a2857c3..5c1c7f5c5 100644
--- a/src/xrt/tracking/hand/mercury/hg_sync.hpp
+++ b/src/xrt/tracking/hand/mercury/hg_sync.hpp
@@ -11,7 +11,7 @@
 #pragma once
 
 #include "hg_interface.h"
-
+#include "hg_debug_instrumentation.hpp"
 
 #include "tracking/t_hand_tracking.h"
 #include "tracking/t_camera_models.h"
@@ -332,30 +332,7 @@ public:
 
 	u_frame_times_widget ft_widget = {};
 
-	struct
-	{
-		bool new_user_event = false;
-		struct u_var_draggable_f32 after_detection_fac;
-		struct u_var_draggable_f32 dyn_radii_fac;
-		struct u_var_draggable_f32 dyn_joint_y_angle_error;
-		struct u_var_draggable_f32 amount_to_lerp_prediction;
-		struct u_var_draggable_f32 amt_use_depth;
-		struct u_var_draggable_f32 mpiou_any;
-		struct u_var_draggable_f32 mpiou_single_detection;
-		struct u_var_draggable_f32 mpiou_double_detection;
-		struct u_var_draggable_f32 max_reprojection_error;
-		struct u_var_draggable_f32 opt_smooth_factor;
-		struct u_var_draggable_f32 max_hand_dist;
-		bool scribble_predictions_into_next_frame = false;
-		bool scribble_keypoint_model_outputs = false;
-		bool scribble_optimizer_outputs = true;
-		bool always_run_detection_model = false; // true
-		bool optimize_hand_size = true;
-		int max_num_outside_view = 6;
-		bool enable_pose_predicted_input = true;
-		bool enable_framerate_based_smoothing = false;
-	} tuneable_values;
-
+	struct hg_tuneable_values tuneable_values;
 
 public:
 	explicit HandTracking();