diff --git a/Disp/DemoDiscreteRgb.cs b/Disp/DemoDiscreteRgb.cs
index 89c89cd..a614120 100644
--- a/Disp/DemoDiscreteRgb.cs
+++ b/Disp/DemoDiscreteRgb.cs
@@ -29,10 +29,10 @@ namespace Sample.Disp
             new Box3d(2, 0, 0, 3, 1, 1).ToDraw_Face().Display(bind);
         }
         /// <inheritdoc/>
-        public void ExpandToBox3d(Box3d dst)
+        public void ExpandToBox3d(ref Box3d dst)
         {
-            dst.Expand(new vec3d_t(0, 0, 0));
-            dst.Expand(new vec3d_t(3, 1, 1));
+            dst = dst.Expanded(new vec3d_t(0, 0, 0));
+            dst = dst.Expanded(new vec3d_t(3, 1, 1));
         }
 
         static void Main()
diff --git a/Disp/DemoPick1.cs b/Disp/DemoPick1.cs
index 08d72be..be05019 100644
--- a/Disp/DemoPick1.cs
+++ b/Disp/DemoPick1.cs
@@ -25,10 +25,10 @@ namespace Sample.Disp
 			bind.PickID = 0;
 		}
         /// <inheritdoc/>
-        public void ExpandToBox3d(Box3d dst)
+        public void ExpandToBox3d(ref Box3d dst)
 		{
-			dst.Expand(new vec3d_t(0, 0, 0));
-			dst.Expand(new vec3d_t(1, 1, 1));
+			dst = dst.Expanded(new vec3d_t(0, 0, 0));
+			dst = dst.Expanded(new vec3d_t(1, 1, 1));
 		}
         /// <inheritdoc/>
         public override void OnMouseEnter(ui_event_type e, DispEngine dispEngine)
diff --git a/Disp/DemoPick2.cs b/Disp/DemoPick2.cs
index 8e1dc00..4174dbb 100644
--- a/Disp/DemoPick2.cs
+++ b/Disp/DemoPick2.cs
@@ -37,10 +37,10 @@ namespace Sample.Disp
 			bind.PickID = 0;
 		}
 		/// <inheritdoc/>
-		public void ExpandToBox3d(Box3d dst)
+		public void ExpandToBox3d(ref Box3d dst)
 		{
-			dst.Expand(new vec3d_t(0, 0, 0));
-			dst.Expand(new vec3d_t(1, 1, 3));
+			dst = dst.Expanded(new vec3d_t(0, 0, 0));
+			dst = dst.Expanded(new vec3d_t(1, 1, 3));
 		}
 		#region IDisposable Support
 		private bool disposedValue = false; // To detect redundant calls
diff --git a/Disp/DemoPickable.cs b/Disp/DemoPickable.cs
index 8f70df4..a682d9d 100644
--- a/Disp/DemoPickable.cs
+++ b/Disp/DemoPickable.cs
@@ -40,9 +40,9 @@ public class DemoPickable : IDisplayee
 		draw.Display(bind);
 	}
 	/// <inheritdoc/>
-	public void ExpandToBox3d(Box3d dst)
+	public void ExpandToBox3d(ref Box3d dst)
 	{
-		draw.ExpandToBox3d(dst);
+		draw.ExpandToBox3d(ref dst);
 	}
 
 	/// <summary>
diff --git a/Disp/DemoSatellite.cs b/Disp/DemoSatellite.cs
index ebd13cc..930323e 100644
--- a/Disp/DemoSatellite.cs
+++ b/Disp/DemoSatellite.cs
@@ -21,8 +21,8 @@ namespace Sample.Disp
 		double angle_moon;
 		DemoSatellite()
 		{
-			sun = Box3d.CenterUnitBox.ScaleFromCenter(4).ToDraw_Face();
-			earth = Box3d.CenterUnitBox.ScaleFromCenter(2).ToDraw_Face();
+			sun = Box3d.CenterUnitBox.ScaledFromCenter(4).ToDraw_Face();
+			earth = Box3d.CenterUnitBox.ScaledFromCenter(2).ToDraw_Face();
 			moon = Box3d.CenterUnitBox.ToDraw_Face();
 		}
         /// <inheritdoc/>
@@ -41,10 +41,10 @@ namespace Sample.Disp
 			bind.ModelMatStack.Pop();
 		}
 		/// <inheritdoc/>
-		public void ExpandToBox3d(Box3d dst)
+		public void ExpandToBox3d(ref Box3d dst)
 		{
-			dst.Expand(new vec3d_t(-14, -14, -2));
-			dst.Expand(new vec3d_t(14, 14, 2));
+			dst = dst.Expanded(new vec3d_t(-14, -14, -2));
+			dst = dst.Expanded(new vec3d_t(14, 14, 2));
 		}
 
 		static void Main()
diff --git a/Disp/DemoUtil.cs b/Disp/DemoUtil.cs
index 46c23c4..fd14fa1 100644
--- a/Disp/DemoUtil.cs
+++ b/Disp/DemoUtil.cs
@@ -33,7 +33,7 @@ public static class DemoUtil
 		try
 		{
 			Box3d box = new Box3d();
-			displayee.ExpandToBox3d(box);
+			displayee.ExpandToBox3d(ref box);
 			Console.WriteLine($"{title}: {displayee.GetType().Name} bounding {box}");
 			Console.WriteLine("Assign it to your canvas' DispEngine.Displayee to see it.");
 		}
diff --git a/Disp/HeidenhainCoordinateEntryDisplayee.cs b/Disp/HeidenhainCoordinateEntryDisplayee.cs
index 5da43b8..de9d7cb 100644
--- a/Disp/HeidenhainCoordinateEntryDisplayee.cs
+++ b/Disp/HeidenhainCoordinateEntryDisplayee.cs
@@ -90,7 +90,7 @@ namespace Sample.Disp
             bind.ModelMatStack.Pop();
         }
         /// <inheritdoc/>
-        public void ExpandToBox3d(Box3d dst)
+        public void ExpandToBox3d(ref Box3d dst)
         {
             HardNcEnv ncEnv = NcEnv;
             if (ncEnv == null || NcEnv.CncBrand != CncBrand.Heidenhain)
@@ -107,7 +107,7 @@ namespace Sample.Disp
                 HeidenhainCycleDef247Q339, HeidenhainCycleDef7Arg, ncEnv);
 
 
-            dst.Expand(-mcXyz_AttacherAtTableMountZero + coordinateMove);
+            dst = dst.Expanded(-mcXyz_AttacherAtTableMountZero + coordinateMove);
         }
         /// <inheritdoc/>
         public Anchor GetAnchor()
diff --git a/Disp/IsoCoordinateEntryDisplayee.cs b/Disp/IsoCoordinateEntryDisplayee.cs
index ffc8315..7ef8e42 100644
--- a/Disp/IsoCoordinateEntryDisplayee.cs
+++ b/Disp/IsoCoordinateEntryDisplayee.cs
@@ -59,7 +59,7 @@ public class IsoCoordinateEntryDisplayee : IAnchoredDisplayee
 		bind.ModelMatStack.Pop();
 	}
 	/// <inheritdoc/>
-	public void ExpandToBox3d(Box3d dst)
+	public void ExpandToBox3d(ref Box3d dst)
 	{
 		HardNcEnv ncEnv = NcEnv;
 		if (ncEnv == null)
@@ -70,7 +70,7 @@ public class IsoCoordinateEntryDisplayee : IAnchoredDisplayee
 		IMachiningEquipment equipment = MillingEquipmentFunc?.Invoke();
 		if (equipment == null || !equipment.TryGetIsoCoordinatePosition(coordinateMove, out vec3d_t attacherPos))
 			return;
-		dst.Expand(attacherPos);
+		dst = dst.Expanded(attacherPos);
 	}
 	/// <inheritdoc/>
 	/// <returns>Table Mount if existed; otherwise, return null.</returns>
diff --git a/Disp/MachiningProjectDisplayee.cs b/Disp/MachiningProjectDisplayee.cs
index a5805a2..4ed3dae 100644
--- a/Disp/MachiningProjectDisplayee.cs
+++ b/Disp/MachiningProjectDisplayee.cs
@@ -239,10 +239,10 @@ public class MachiningProjectDisplayee : IDisplayee, IGetAnchor
 		bind.PopColor();
 	}
 	/// <inheritdoc/>
-	public void ExpandToBox3d(Box3d dst)
+	public void ExpandToBox3d(ref Box3d dst)
 	{
 		//Console.WriteLine($"dst.A: {dst}");
-		LocalProjectService?.MachiningEquipment?.GetAsmb()?.ExpandToBox3d(dst,
+		LocalProjectService?.MachiningEquipment?.GetAsmb()?.ExpandToBox3d(ref dst,
 				GetAnchor(),
 				GetAnchoredDisplayeeList().ToArray());
 		//Console.WriteLine($"dst.B: {dst}");