diff --git a/SpectrumView.pas b/SpectrumView.pas
index b435d35..eb2e084 100644
--- a/SpectrumView.pas
+++ b/SpectrumView.pas
@@ -48,6 +48,7 @@ type
     FSmBitmap:        TBitmap;
     FRulerLastFreq:   Double;
     FRulerLastVfo:    Double;
+    FRulerLastSpan:   Double;
 
     // ── Radio state ───────────────────────────────────────────────────────────
     FVfoA:          Double;
@@ -513,7 +514,7 @@ procedure TSpectrumView.SetRulerSize(W, H: Integer);
 begin
   if (W <= 0) or (H <= 0) then Exit;
   FRulerBitmap.SetSize(W, H);
-  FRulerLastFreq := -1.0; FRulerLastVfo := -1.0;
+  FRulerLastFreq := -1.0; FRulerLastVfo := -1.0; FRulerLastSpan := -1.0;
 end;
 
 function TSpectrumView.SpectrumBitmapWidth: Integer;
@@ -533,7 +534,7 @@ end;
 
 procedure TSpectrumView.InvalidateRulerCache;
 begin
-  FRulerLastFreq := -1.0; FRulerLastVfo := -1.0;
+  FRulerLastFreq := -1.0; FRulerLastVfo := -1.0; FRulerLastSpan := -1.0;
 end;
 
 procedure TSpectrumView.ResetSpectrumBuf;
@@ -570,7 +571,8 @@ end;
 function TSpectrumView.NeedsRulerRedraw: Boolean;
 begin
   Result := (Abs(FCenterFreq - FRulerLastFreq) >= 0.5) or
-            (Abs(ActiveVfoFreq - FRulerLastVfo) >= 0.5);
+            (Abs(ActiveVfoFreq - FRulerLastVfo) >= 0.5) or
+            (Abs(FSpanHz - FRulerLastSpan) >= 1.0);
 end;
 
 // ────────────────────────────────────────────────────────────────────────────
@@ -854,8 +856,9 @@ begin
   W := FPbRuler.Width; H := FPbRuler.Height;
   if (W <= 0) or (H <= 0) then Exit;
   if (Abs(FCenterFreq - FRulerLastFreq) < 0.5) and
-     (Abs(ActiveVfoFreq - FRulerLastVfo) < 0.5) then Exit;
-  FRulerLastFreq := FCenterFreq; FRulerLastVfo := ActiveVfoFreq;
+     (Abs(ActiveVfoFreq - FRulerLastVfo) < 0.5) and
+     (Abs(FSpanHz - FRulerLastSpan) < 1.0) then Exit;
+  FRulerLastFreq := FCenterFreq; FRulerLastVfo := ActiveVfoFreq; FRulerLastSpan := FSpanHz;
   if (FRulerBitmap.Width <> W) or (FRulerBitmap.Height <> H) then
     FRulerBitmap.SetSize(W, H);
   C := FRulerBitmap.Canvas;