diff --git a/global_data.cpp b/global_data.cpp
index 2e5e7ed..89a2be4 100644
--- a/global_data.cpp
+++ b/global_data.cpp
@@ -54,11 +54,14 @@ radar_management_structure radar_management[RADAR_COUNT] = {
 // Components: Thread 1, Traffic Cop (Thread 2), all scope renderers
 int current_radar = RADAR_NONE;
 
-// Range settnigs for each radar
-int chain_home_range_setting;
-int ascope_range_setting;
-int traffic_control_range_setting;
-int police_boat range_setting; 
+// Range step indices — 0 = lowest (shortest) range step for each scope.
+// Incremented/decremented by the o/p keyboard handler in Thread 1.
+// Chain Home is fixed-range; its index exists for consistency but is unused.
+// Components: Thread 1 keyboard handler, each scope renderer
+int chain_home_range_setting    = 0;
+int ascope_range_setting        = 0;
+int traffic_control_range_setting = 0;
+int police_boat_range_setting   = 0;
 
 /* ============================================================
  * THREAD MUTEXES
diff --git a/include/data_structure_and_constants.h b/include/data_structure_and_constants.h
index c167fce..1451769 100644
--- a/include/data_structure_and_constants.h
+++ b/include/data_structure_and_constants.h
@@ -63,7 +63,9 @@ struct target_data_structure {
 };
 
 /* Lean SSBO payload uploaded to shaders via SSBO layout(std430).
- * String fields are stripped before upload.
+ * String fields and timestamp are stripped before upload — the Traffic Cop
+ * discards stale targets (>1 hour) on the CPU, so the GPU needs no timestamp.
+ * time_t (int64) has no matching GLSL std430 type without an extension.
  * Components: Thread 1 (shader upload), all radar scope shaders */
 struct ssbo_target_information {
     float target_x;               // Cartesian offset X, meters from radar
@@ -72,7 +74,6 @@ struct ssbo_target_information {
     float beam;                   // meters
     float course;                 // radians, true north
     float altitude;               // meters; 0 for surface vessels
-    time_t timestamp;
     float current_reflectivity;   // derived from vessel_type
     float height_estimate;        // derived from vessel_type
     float noiseglint;             // derived from vessel_type
@@ -213,3 +214,30 @@ extern float uniform_bearing_cursor;
 // Components: Marine A-scope
 extern float uniform_marine_a_bearing;
 
+/* ============================================================
+ * RANGE STEP INDICES
+ * Track which discrete range step is currently selected per scope.
+ * Indexed from 0; map to the MARINE_A_SCOPE_RANGE_STEP_* and
+ * PPI_*_RANGE_STEP_* constants defined in settings.h.
+ * Defined in global_data.cpp; extern declared here.
+ * Components: Thread 1 (keyboard o/p handler), each scope renderer
+ * ============================================================ */
+
+// Chain Home range is fixed (CHAIN_HOME_MAX_RANGE_KM in settings.h); this index
+// is defined for structural consistency but the keyboard o/p handler ignores it
+// when current_radar == RADAR_CHAIN_HOME.
+// Components: Thread 1 keyboard handler (no-op for Chain Home)
+extern int chain_home_range_setting;
+
+// Marine A-scope range step index (0 = 3 nm, 3 = 24 nm)
+// Components: Marine A-scope, Thread 1 keyboard handler
+extern int ascope_range_setting;
+
+// Marine traffic control PPI range step index (0 = 3 nm, 4 = 48 nm)
+// Components: Marine traffic control scope, Thread 1 keyboard handler
+extern int traffic_control_range_setting;
+
+// Police boat PPI range step index (0 = 1.5 nm, 4 = 24 nm)
+// Components: Police boat scope, Thread 1 keyboard handler
+extern int police_boat_range_setting;
+