diff --git a/game/reconstructed/btl4gaug.cpp b/game/reconstructed/btl4gaug.cpp
index 993a781..18384eb 100644
--- a/game/reconstructed/btl4gaug.cpp
+++ b/game/reconstructed/btl4gaug.cpp
@@ -1552,13 +1552,149 @@ void
 //      segmentSpan = (int)( (float)(|n|/(|n|-1)) * 0.75f )    // _DAT_004c62d4
 // Deleting-dtor thunk @004c66b3 -> FUN_00474094 (arc base dtor).
 //
-// @004c62fc Make / @004c6394 ctor (vtable PTR_FUN_0051898c) -- SegmentArcRatio:
-// derives from the second MUNGA L4 arc primitive (FUN_00473f44) and adds TWO
-// GaugeConnectionDirectOf<Scalar> feeds (numerator @0x30, denominator @0x31,
-// FUN_00474855 x2); precomputes segmentSpan with _DAT_004c6484 (0.75f).
-// Make @004c62fc allocates 0xcc and supplies the arc geometry resources
-// (DAT_00517eb0..00518158) and the name "SegmentArcRatio".
-// Deleting-dtor thunk @004c668d -> FUN_00474094.
+//###########################################################################
+//   SegmentArcRatio   @004c62fc Make / @004c6394 ctor / @004c6488 Execute
+//                     (vtable PTR_FUN_0051898c; base = engine SegmentArc)
 //
+// A segmented arc dial (config keyword "segmentArcRatio").  Two Scalar
+// connections drive it -- numerator (value) and denominator (max) -- and Execute
+// lights numerator/denominator of the arc.  Used for the cockpit SPEED arc
+// (config binds numerator=LinearSpeed, denominator=MaxRunSpeed), so the arc
+// sweeps as the mech accelerates.  Unlike VertTwoPartBar, the drawing is
+// inherited from the engine SegmentArc base -- this class only computes the
+// [0,1] fill fraction into the base's currentValue, then delegates the render.
+//###########################################################################
+
+MethodDescription
+	SegmentArcRatio::methodDescription =
+	{
+		"segmentArcRatio",
+		SegmentArcRatio::Make,
+		{
+			//
+			// CFG shape (L4GAUGE.CFG:4964):
+			//   segmentArcRatio( rate, mode, inner,outer, deg0,deg1, segs,
+			//                    bg,fg, valueAttr, maxAttr )
+			//   e.g. segmentArcRatio(C,ModeAlwaysActive,32,39,0,360,36,0,2,
+			//                        LinearSpeed, MaxRunSpeed);
+			//
+			{ ParameterDescription::typeRate,      NULL },	// rate ID
+			{ ParameterDescription::typeModeMask,  NULL },	// mode mask
+			{ ParameterDescription::typeScalar,    NULL },	// inner radius
+			{ ParameterDescription::typeScalar,    NULL },	// outer radius
+			{ ParameterDescription::typeScalar,    NULL },	// start angle (deg)
+			{ ParameterDescription::typeScalar,    NULL },	// end angle (deg)
+			{ ParameterDescription::typeInteger,   NULL },	// segment count (+dir)
+			{ ParameterDescription::typeColor,     NULL },	// background colour
+			{ ParameterDescription::typeColor,     NULL },	// foreground colour
+			{ ParameterDescription::typeAttribute, NULL },	// numerator (value)
+			{ ParameterDescription::typeAttribute, NULL },	// denominator (max)
+			PARAMETER_DESCRIPTION_END
+		}
+	};
+
+//
+// @004c62fc -- Make.  Allocate + construct; no resource to verify (returns True).
+//
+Logical
+	SegmentArcRatio::Make(
+		int					display_port_index,
+		Vector2DOf<int>		position,
+		Entity				* /*entity -- unused*/,
+		GaugeRenderer		*gauge_renderer
+	)
+{
+	ParameterDescription *p = methodDescription.parameterList;
+
+	SegmentArcRatio *gauge = (SegmentArcRatio *)operator new(0xcc);	// FUN_00402298(0xcc)
+	if (gauge != NULL)
+	{
+		new (gauge) SegmentArcRatio(				// FUN_004c6394
+			p[0].data.rate, p[1].data.modeMask,
+			(L4GaugeRenderer *)gauge_renderer,
+			display_port_index,						// graphics_port_number
+			position.x, position.y,					// centre
+			p[2].data.scalar, p[3].data.scalar,		// inner, outer radius
+			p[4].data.scalar, p[5].data.scalar,		// start, end angle
+			p[6].data.integer,						// segment count (+dir)
+			p[7].data.color, p[8].data.color,		// bg, fg
+			(Scalar *)p[9].data.attributePointer,	// numerator source
+			(Scalar *)p[10].data.attributePointer,	// denominator source
+			"SegmentArcRatio");
+	}
+	return True;									// binary returns 1 unconditionally
+}
+
+//
+// @004c6394 -- ctor.  Engine SegmentArc base (inner0==inner1, outer0==outer1 --
+// the Make duplicates them, so the arc has a constant radius); precompute the
+// span factor and wire the two Scalar connections.
+//
+SegmentArcRatio::SegmentArcRatio(
+	GaugeRate			rate,
+	ModeMask			mode_mask,
+	L4GaugeRenderer		*renderer_in,
+	int					graphics_port_number,
+	int					center_x,
+	int					center_y,
+	Scalar				inner,
+	Scalar				outer,
+	Scalar				deg0,
+	Scalar				deg1,
+	int					number_of_segs,
+	int					background_color,
+	int					foreground_color,
+	Scalar				*numerator_pointer,
+	Scalar				*denominator_pointer,
+	const char			*identification_string
+):
+	SegmentArc(rate, mode_mask, renderer_in, 0,					// FUN_00473f44 (owner_ID 0)
+			   graphics_port_number, center_x, center_y,
+			   inner, outer, inner, outer,						// inner0/outer0 == inner1/outer1
+			   deg0, deg1, number_of_segs,
+			   background_color, foreground_color,
+			   True,											// use_thick_lines (binary param_20 = 1)
+			   identification_string)
+{
+	// segmentSpan = (Scalar)(|n| / (|n|-1)) * 0.75f  -- |n|/(|n|-1) is INTEGER
+	// division (== 1 for n>=2), so this is 0.75 for the 36-segment speed arc.
+	int n = (number_of_segs < 0) ? -number_of_segs : number_of_segs;	// @0xC8
+	segmentSpan = (Scalar)(n / (n - 1)) * 0.75f;					// _DAT_004c6484 = 0.75f
+
+	AddConnection(new GaugeConnectionDirectOf<Scalar>(0, &numerator,   numerator_pointer));	// @0xC0
+	AddConnection(new GaugeConnectionDirectOf<Scalar>(0, &denominator, denominator_pointer));	// @0xC4
+}
+
+//
+// @004c668d -- deleting-dtor thunk.  Connections + arc base are released by the
+// implicit base-dtor chain (FUN_00474094); no own teardown.
+//
+SegmentArcRatio::~SegmentArcRatio()
+{
+}
+
+//
+// @004c6488 -- Execute.  currentValue = clamp(|numerator/denominator * span|,0,1);
+// then delegate to the engine SegmentArc::Execute (0x474300) which lights that
+// fraction of the segments.  (x87 recovered by disassembly: FUN_004dcd00 = fabs.)
+//
+void
+	SegmentArcRatio::Execute()
+{
+	if (denominator < 1.0f)								// guard div-by-tiny / unpowered
+	{
+		currentValue = 0.0f;
+	}
+	else
+	{
+		currentValue = numerator / denominator * segmentSpan;
+		if (currentValue < 0.0f) currentValue = -currentValue;	// FUN_004dcd00 = fabs
+		if (currentValue < 0.0f)
+			currentValue = 0.0f;
+		else if (currentValue > 1.0f)
+			currentValue = 1.0f;
+	}
+	SegmentArc::Execute();								// 0x474300 -- the base draw
+}
 
 // === btl4gau2.cpp begins at @004c6798 (SeekVoltage gauge) -- not part of this TU.
diff --git a/game/reconstructed/btl4gaug.hpp b/game/reconstructed/btl4gaug.hpp
index 0b8ece0..b9a6809 100644
--- a/game/reconstructed/btl4gaug.hpp
+++ b/game/reconstructed/btl4gaug.hpp
@@ -518,16 +518,28 @@
 	};
 
 	class SegmentArcRatio :
-		public SegmentArc							// MUNGA L4 base (FUN_00473f44; engine class SegmentArc)
+		public SegmentArc							// MUNGA L4 base (engine SegmentArc, L4GAUGE.cpp:4827)
 	{
 	public:
+		// Registered in BTL4MethodDescription[] (btl4grnd.cpp) as "segmentArcRatio".
+		static MethodDescription methodDescription;
+
 		static Logical Make(int, Vector2DOf<int>, Entity *, GaugeRenderer *);	// @004c62fc
-		SegmentArcRatio(/* ...arc geometry... */);	// @004c6394
+		SegmentArcRatio(							// @004c6394
+			GaugeRate, ModeMask, L4GaugeRenderer *, int graphics_port_number,
+			int center_x, int center_y,
+			Scalar inner, Scalar outer, Scalar deg0, Scalar deg1,
+			int number_of_segs, int background_color, int foreground_color,
+			Scalar *numerator_pointer, Scalar *denominator_pointer,
+			const char *identification_string);
 		~SegmentArcRatio();							// dtor thunk @004c668d
+
+		void	Execute();							// @004c6488 (ratio -> currentValue -> SegmentArc::Execute)
+
 	protected:
 		Scalar	numerator;							// @0xC0  this[0x30]  (connection)
 		Scalar	denominator;						// @0xC4  this[0x31]  (connection)
-		int		segmentSpan;						// @0xC8  this[0x32]
+		Scalar	segmentSpan;						// @0xC8  this[0x32]  (float, read by Execute)
 	};
 
 #endif
diff --git a/game/reconstructed/btl4grnd.cpp b/game/reconstructed/btl4grnd.cpp
index a0b3117..19cb447 100644
--- a/game/reconstructed/btl4grnd.cpp
+++ b/game/reconstructed/btl4grnd.cpp
@@ -135,6 +135,7 @@ MethodDescription
 			&ColorMapperMultiArmor::methodDescription,	// "colorMapperMultiArmor" -- worst-of-8-zones tint
 			&ColorMapperCritical::methodDescription,	// "cmCrit" -- subsystem-critical-state tint
 			&VertTwoPartBar::methodDescription,			// "vertBar" -- vertical fill bar (coolant/heat)
+			&SegmentArcRatio::methodDescription,		// "segmentArcRatio" -- segmented arc dial (speed)
 			&BTL4ChainToPrevious
 		};