diff --git a/.github/workflows/smv-direct-inno-preview.yml b/.github/workflows/smv-direct-inno-preview.yml
index 5b6e30fcd..184801d43 100644
--- a/.github/workflows/smv-direct-inno-preview.yml
+++ b/.github/workflows/smv-direct-inno-preview.yml
@@ -4,7 +4,7 @@ name: Direct Inno SMV Preview EXE
 # Trusted, narrowly scoped branch only. Stable release is never modified.
 on:
   push:
-    branches: [feat/smv-sharp-latest-p0-20261022]
+    branches: [feat/smv-real-arstack-timebase-override-20261022]
 
 permissions:
   contents: write
@@ -15,7 +15,7 @@ concurrency:
 
 jobs:
   direct-preview:
-    if: github.repository == 'masarray/arsas' && github.ref == 'refs/heads/feat/smv-sharp-latest-p0-20261022'
+    if: github.repository == 'masarray/arsas' && github.ref == 'refs/heads/feat/smv-real-arstack-timebase-override-20261022'
     runs-on: windows-latest
     timeout-minutes: 65
     defaults:
diff --git a/Services/SmvLiveCaptureService.cs b/Services/SmvLiveCaptureService.cs
index f94d8f6ce..4aaa0b19f 100644
--- a/Services/SmvLiveCaptureService.cs
+++ b/Services/SmvLiveCaptureService.cs
@@ -16,6 +16,8 @@ public sealed record SmvLiveCaptureOptions
     public required string AdapterSelector { get; init; }
     public double NominalFrequencyHz { get; init; } = 50;
     public int Cycles { get; init; } = 2;
+    // Display-only assumption, NEVER a verified source sampling rate.
+    public int? DisplaySamplesPerCycleOverride { get; init; }
     public int MaximumChannels { get; init; } = 8;
     public int MaximumStreams { get; init; } = 32;
     public int RefreshMilliseconds { get; init; } = 200;
@@ -51,7 +53,8 @@ public async Task RunAsync(SmvLiveCaptureOptions options,
             options.Cycles is < 1 or > 10 ||
             options.MaximumChannels is < 1 or > 16 ||
             options.MaximumStreams is < 1 or > 64 ||
-            options.RefreshMilliseconds is < 100 or > 2000)
+            options.RefreshMilliseconds is < 100 or > 2000 ||
+            options.DisplaySamplesPerCycleOverride is not (null or 80 or 256))
             throw new ArgumentOutOfRangeException(nameof(options), "Invalid bounded SV capture configuration.");
 
         var catalog = new SmvLiveStreamCatalog(options);
@@ -416,6 +419,21 @@ private void Configure(SampledValueAsdu asdu, int payloadLength)
             IsFixedLegacyProtectionLayout = groups && payloadLength == 64,
             TrustedNominalFrequencyHz = _options.NominalFrequencyHz
         });
+        // A real SV publisher may omit smpRate/smpMod and provide unusable NIC
+        // timestamp cadence. Only an EXPLICIT operator-selected display window
+        // can bypass rate verification. Raw samples and smpCnt discontinuity
+        // checks remain mandatory; this MUST NOT claim MU/PTP synchronization.
+        if (!_timebase.IsResolved && _options.DisplaySamplesPerCycleOverride is int assumed)
+        {
+            _timebase = new SvTimebaseResolution
+            {
+                SamplesPerCycle = assumed,
+                NominalFrequencyHz = _options.NominalFrequencyHz,
+                Source = SvTimebaseSource.ObservedLegacyProtectionRate,
+                Reason = $"ASSUMED display window {assumed} samples/cycle from operator selection. " +
+                    "Sample rate and PTP sync NOT verified; counter continuity enforced."
+            };
+        }
         if (!_timebase.IsResolved)
         {
             _length = 0;
@@ -430,6 +448,20 @@ private void Configure(SampledValueAsdu asdu, int payloadLength)
     private void AllocateResolvedWindow()
     {
         var length = (long)_timebase!.SamplesPerCycle.GetValueOrDefault() * _options.Cycles;
+        if ((length is < 4 or > 4096) &&
+            _options.DisplaySamplesPerCycleOverride is int chosen &&
+            _timebase is { IsResolved: true })
+        {
+            _timebase = new SvTimebaseResolution
+            {
+                SamplesPerCycle = chosen,
+                NominalFrequencyHz = _options.NominalFrequencyHz,
+                Source = SvTimebaseSource.ObservedLegacyProtectionRate,
+                Reason = $"ASSUMED display window {chosen} samples/cycle (conflicting/unusable declared rate). " +
+                    "Operator-selected, NOT verified sampling rate or PTP synchronization."
+            };
+            length = (long)chosen * _options.Cycles;
+        }
         if (length is < 4 or > 4096 || _wordIndexes.Length == 0)
         {
             _length = 0;
diff --git a/Views/SmvInlineViewer.xaml b/Views/SmvInlineViewer.xaml
index 4914360dc..a1a0c2d75 100644
--- a/Views/SmvInlineViewer.xaml
+++ b/Views/SmvInlineViewer.xaml
@@ -97,6 +97,8 @@
                     <ColumnDefinition Width="Auto"/>
                     <ColumnDefinition Width="7"/>
                     <ColumnDefinition Width="Auto"/>
+                    <ColumnDefinition Width="10"/>
+                    <ColumnDefinition Width="Auto"/>
                     <ColumnDefinition Width="*"/>
                 </Grid.ColumnDefinitions>
                 <StackPanel VerticalAlignment="Center">
@@ -138,6 +140,14 @@
                     <ComboBoxItem Content="Raw counts" Tag="Raw"/>
                     <ComboBoxItem Content="9-2LE · V/A" Tag="NineTwoLe"/>
                 </ComboBox>
+                <ComboBox x:Name="TimebaseCombo" Grid.Column="16"
+                          Style="{StaticResource ModernComboBox}" Width="126" Height="33"
+                          MinHeight="33" Padding="8,2" FontSize="10.5" SelectedIndex="0"
+                          ToolTip="Auto proves rate from metadata or NIC timing. 80/256 is an unverified display-only assumption for problematic field streams.">
+                    <ComboBoxItem Content="Timebase Auto" Tag="Auto"/>
+                    <ComboBoxItem Content="80 / cycle" Tag="80"/>
+                    <ComboBoxItem Content="256 / cycle" Tag="256"/>
+                </ComboBox>
                 <Button x:Name="StartButton" Grid.Column="6"
                         Style="{StaticResource PrimaryButton}" Padding="12,6"
                         MinHeight="33" MinWidth="82" Height="33"
diff --git a/Views/SmvInlineViewer.xaml.cs b/Views/SmvInlineViewer.xaml.cs
index ec9b19d63..848d45625 100644
--- a/Views/SmvInlineViewer.xaml.cs
+++ b/Views/SmvInlineViewer.xaml.cs
@@ -172,6 +172,7 @@ private async void Start_Click(object sender, RoutedEventArgs e)
         StopButton.IsEnabled = true;
         AdapterCombo.IsEnabled = false;
         FrequencyCombo.IsEnabled = false;
+        TimebaseCombo.IsEnabled = false;
         _freshness.Start();
 
         var hz = FrequencyCombo.SelectedItem is ComboBoxItem item &&
@@ -181,6 +182,9 @@ private async void Start_Click(object sender, RoutedEventArgs e)
             AdapterSelector = adapter.Selector,
             NominalFrequencyHz = hz,
             Cycles = 2,
+            DisplaySamplesPerCycleOverride =
+                int.TryParse((TimebaseCombo.SelectedItem as ComboBoxItem)?.Tag?.ToString(), out var chosenSpc)
+                    ? chosenSpc : null,
             MaximumChannels = 8,
             MaximumStreams = 32,
             RefreshMilliseconds = 200
@@ -214,6 +218,7 @@ await _service.RunAsync(options,
                 StopButton.IsEnabled = false;
                 AdapterCombo.IsEnabled = true;
                 FrequencyCombo.IsEnabled = true;
+        TimebaseCombo.IsEnabled = true;
                 IsLiveSnapshot = false;
                 Notify(nameof(IsLiveSnapshot));
                 WaveformStatus = _visibleSnapshot is null
@@ -413,6 +418,8 @@ private void UpdateUnitPresentation(bool redrawWaveform)
             CurrentWaveform = SmvDigSubPresentationAdapter.BuildWaveform(snapshot, profile);
             Notify(nameof(CurrentWaveform));
             WaveformStatus =
+                (snapshot.TimebaseReason.StartsWith("ASSUMED", StringComparison.OrdinalIgnoreCase)
+                    ? "ASSUMED timebase · rate/PTP unverified · " : string.Empty) +
                 $"Received {snapshot.CapturedSamples:N0} coherent samples • {snapshot.SamplesPerCycle} samples/cycle • " +
                 (profile == SmvDisplayUnits.NineTwoLe
                     ? "9-2LE operator-selected engineering display"
diff --git a/tests/ARSAS.Tests/SmvArsasThemeRegressionTests.cs b/tests/ARSAS.Tests/SmvArsasThemeRegressionTests.cs
index 8f663b582..97f00e404 100644
--- a/tests/ARSAS.Tests/SmvArsasThemeRegressionTests.cs
+++ b/tests/ARSAS.Tests/SmvArsasThemeRegressionTests.cs
@@ -15,7 +15,7 @@ public void SmvWorkspace_UsesMainWorkstationResourcesForEveryOperatorControl()
         Assert.Contains("Style=\"{StaticResource SoftButton}\"", x);
         Assert.Contains("Style=\"{StaticResource IedIconButton}\"", x);
         Assert.Contains("FontFamily=\"{StaticResource AppFontFamily}\"", x);
-        Assert.Equal(6, Count(x, "Style=\"{StaticResource ModernComboBox}\""));
+        Assert.Equal(7, Count(x, "Style=\"{StaticResource ModernComboBox}\""));
         Assert.Contains("<ListBox x:Name=\"StreamList\"", x);
         Assert.Contains("ItemContainerStyle=\"{StaticResource SmvStreamItem}\"", x);
         Assert.Contains("VirtualizationMode=\"Recycling\"", x);
diff --git a/tests/ARSAS.Tests/SmvArstackUnverifiedDisplayWindowTests.cs b/tests/ARSAS.Tests/SmvArstackUnverifiedDisplayWindowTests.cs
new file mode 100644
index 000000000..56e574d1b
--- /dev/null
+++ b/tests/ARSAS.Tests/SmvArstackUnverifiedDisplayWindowTests.cs
@@ -0,0 +1,74 @@
+using System.Buffers.Binary;
+using AR.Iec61850.Ethernet;
+using AR.Iec61850.SampledValues;
+using ArIED61850Tester.Services;
+
+namespace ARSAS.Tests;
+
+public sealed class SmvArstackUnverifiedDisplayWindowTests
+{
+    private static SampledValuesFrame Frame(int counter) {
+        var bytes = new byte[64];
+        for(var channel=0;channel<8;channel++)
+            BinaryPrimitives.WriteInt32BigEndian(bytes.AsSpan(channel*8,4),
+                (int)(1000*Math.Sin(2*Math.PI*counter/80.0)));
+        return new SampledValuesFrame {
+            Source=MacAddress.Parse("E8:F6:0A:E0:C5:3F"),
+            Destination=MacAddress.Parse("01:0C:CD:04:00:01"),
+            AppId=0x4000,
+            Pdu=new SampledValuesPdu { Asdus=[
+                new SampledValueAsdu {
+                    SvId="ARSTACK_SV01", DataSetReference="MU/LLN0$PhsMeas1",
+                    SampleCount=(ushort)counter,SamplePayload=bytes,
+                    SampleRate=null,SampleMode=null
+                }
+            ]}
+        };
+    }
+
+    [Fact]
+    public void UnreliableFrozenNicTimestamps_ExplicitDisplayOnly80StillRendersRealCounterCoherentSamples()
+    {
+        var t=DateTimeOffset.UtcNow;
+        var options=new SmvLiveCaptureOptions {
+            AdapterSelector="fixture", NominalFrequencyHz=50,
+            Cycles=2,DisplaySamplesPerCycleOverride=80
+        };
+        var cat=new SmvLiveStreamCatalog(options);
+        for(var i=0;i<340;i++)
+            cat.Receive(Frame(i),t);
+        var identity=Assert.Single(cat.Publish(null,t).Streams);
+        var snapshot=Assert.IsType<SmvSnapshotResult>(
+            cat.Publish(identity.Key,t).SelectedSnapshot);
+        Assert.True(snapshot.IsCleanProof);
+        Assert.Equal(80,snapshot.SamplesPerCycle);
+        Assert.Equal(160,snapshot.CapturedSamples);
+        Assert.Contains("ASSUMED",snapshot.TimebaseReason);
+        Assert.Contains("NOT verified",snapshot.TimebaseReason,StringComparison.OrdinalIgnoreCase);
+    }
+
+    [Fact]
+    public void NoOperatorOverride_FrozenClockStillFailsClosed()
+    {
+        var t=DateTimeOffset.UtcNow;
+        var cat=new SmvLiveStreamCatalog(new SmvLiveCaptureOptions { AdapterSelector="fixture" });
+        for(var i=0;i<340;i++)
+            cat.Receive(Frame(i),t);
+        var selected=Assert.Single(cat.Publish(null,t).Streams);
+        Assert.Null(cat.Publish(selected.Key,t).SelectedSnapshot);
+    }
+
+    [Fact]
+    public void OperatorOverride_StillRejectsGappedCounterWindows()
+    {
+        var t=DateTimeOffset.UtcNow;
+        var cat=new SmvLiveStreamCatalog(new SmvLiveCaptureOptions {
+            AdapterSelector="fixture",DisplaySamplesPerCycleOverride=80
+        });
+        for(var i=0;i<100;i++) cat.Receive(Frame(i),t);
+        for(var i=105;i<220;i++) cat.Receive(Frame(i),t);
+        var selected=Assert.Single(cat.Publish(null,t).Streams);
+        Assert.Null(cat.Publish(selected.Key,t).SelectedSnapshot);
+        Assert.True(selected.Gaps>0);
+    }
+}