diff --git a/Plant3D2026/P_Rec_Annot/src/PRecAnnot.Abstractions/Contracts.cs b/Plant3D2026/P_Rec_Annot/src/PRecAnnot.Abstractions/Contracts.cs
index 14f2939..38762d2 100644
--- a/Plant3D2026/P_Rec_Annot/src/PRecAnnot.Abstractions/Contracts.cs
+++ b/Plant3D2026/P_Rec_Annot/src/PRecAnnot.Abstractions/Contracts.cs
@@ -64,6 +64,10 @@ public sealed record LineNumberApplyResult(int Created, int Updated, int Unchang
 public sealed record LineNumberListApplyPreflight(string StableId, AnnotationPoint Position, double Rotation, IReadOnlyList<LineNumberApplyPreflight> Rows);
 public sealed record LineNumberPreviewResult(bool Success, LineNumberCommandPlan? Plan, IReadOnlyList<LineNumberApplyPreflight> Apply, string? FailureCode = null);
 public sealed record LineNumberCandidateReadResult(bool Success, LineNumberCandidate? Candidate, string? FailureCode = null);
+public sealed record ElevationCandidate(string StableId, double ModelElevation, double DatumOffset, AnnotationPoint Position, double Rotation, string Layer, string TextStyle);
+public sealed record ExistingElevationAnnotation(string StableId, string SourceStableId, string Text, AnnotationPoint Position);
+public sealed record ElevationAnnotationOperation(string StableId, AnnotationOperationKind Kind, string? Text, AnnotationPoint Position, double Rotation, string Layer, string TextStyle, IReadOnlyList<string> Reasons);
+public sealed record ElevationAnnotationPlan(IReadOnlyList<ElevationAnnotationOperation> Operations);
 public sealed record LineNumberTextAsset(string Layer, string TextStyle, double Size, string TextValue, Point2Dto Position);
 public sealed record LineNumberLineAsset(string Layer, Point2Dto Start, Point2Dto End);
 public sealed record LineNumberMarkerAsset(string Layer, double MaskScaleFactor, IReadOnlyList<LineNumberTextAsset> Texts, IReadOnlyList<LineNumberLineAsset> Lines);
diff --git a/Plant3D2026/P_Rec_Annot/src/PRecAnnot.Core/ElevationAnnotationPlanner.cs b/Plant3D2026/P_Rec_Annot/src/PRecAnnot.Core/ElevationAnnotationPlanner.cs
new file mode 100644
index 0000000..ef3512e
--- /dev/null
+++ b/Plant3D2026/P_Rec_Annot/src/PRecAnnot.Core/ElevationAnnotationPlanner.cs
@@ -0,0 +1,39 @@
+using PRecAnnot.Abstractions;
+
+namespace PRecAnnot.Core;
+
+public sealed class ElevationAnnotationPlanner
+{
+    public ElevationAnnotationPlan Build(IEnumerable<ElevationCandidate> candidates, IEnumerable<ExistingElevationAnnotation> existing)
+    {
+        var known = existing.GroupBy(value => value.SourceStableId, StringComparer.OrdinalIgnoreCase)
+            .ToDictionary(group => group.Key, group => group.ToArray(), StringComparer.OrdinalIgnoreCase);
+        var seen = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
+        var operations = new List<ElevationAnnotationOperation>();
+        foreach (var candidate in candidates.OrderBy(value => value.StableId, StringComparer.Ordinal))
+        {
+            if (!seen.Add(candidate.StableId))
+            {
+                operations.Add(new(candidate.StableId, AnnotationOperationKind.Conflict, null, candidate.Position, candidate.Rotation, candidate.Layer, candidate.TextStyle, ["DUPLICATE_CANDIDATE"]));
+                continue;
+            }
+            if (string.IsNullOrWhiteSpace(candidate.Layer) || string.IsNullOrWhiteSpace(candidate.TextStyle) || double.IsNaN(candidate.ModelElevation) || double.IsInfinity(candidate.ModelElevation))
+            {
+                operations.Add(new(candidate.StableId, AnnotationOperationKind.Skip, null, candidate.Position, candidate.Rotation, candidate.Layer, candidate.TextStyle, ["ELEVATION_CANDIDATE_INVALID"]));
+                continue;
+            }
+            var text = LegacyElevationFormatter.Calculate(candidate.ModelElevation, candidate.DatumOffset);
+            var matches = known.GetValueOrDefault(candidate.StableId, []);
+            if (matches.Length > 1)
+            {
+                operations.Add(new(candidate.StableId, AnnotationOperationKind.Conflict, text, candidate.Position, candidate.Rotation, candidate.Layer, candidate.TextStyle, ["DUPLICATE_EXISTING_ANNOTATION"]));
+                continue;
+            }
+            if (matches.Length == 1 && string.Equals(matches[0].Text, text, StringComparison.Ordinal) && matches[0].Position == candidate.Position)
+                operations.Add(new(candidate.StableId, AnnotationOperationKind.Skip, text, candidate.Position, candidate.Rotation, candidate.Layer, candidate.TextStyle, ["ALREADY_CURRENT"]));
+            else
+                operations.Add(new(candidate.StableId, matches.Length == 1 ? AnnotationOperationKind.Update : AnnotationOperationKind.Create, text, candidate.Position, candidate.Rotation, candidate.Layer, candidate.TextStyle, Array.Empty<string>()));
+        }
+        return new(operations);
+    }
+}
diff --git a/Plant3D2026/P_Rec_Annot/tests/PRecAnnot.Core.Tests/ElevationAnnotationPlannerTests.cs b/Plant3D2026/P_Rec_Annot/tests/PRecAnnot.Core.Tests/ElevationAnnotationPlannerTests.cs
new file mode 100644
index 0000000..ce80fce
--- /dev/null
+++ b/Plant3D2026/P_Rec_Annot/tests/PRecAnnot.Core.Tests/ElevationAnnotationPlannerTests.cs
@@ -0,0 +1,28 @@
+using PRecAnnot.Abstractions;
+using PRecAnnot.Core;
+
+namespace PRecAnnot.Core.Tests;
+
+public sealed class ElevationAnnotationPlannerTests
+{
+    [Fact]
+    public void PlansCreateUpdateAlreadyCurrentAndConflictsDeterministically()
+    {
+        var a = new ElevationCandidate("a", 5, 0, new(0, 0), 0, "PXP", "GOSTC");
+        var b = new ElevationCandidate("b", 10, 0, new(1, 0), 0, "PXP", "GOSTC");
+        var plan = new ElevationAnnotationPlanner().Build([b, a, a], [new("old-a", "a", "+0,005", new(0, 0)), new("old-b1", "b", "+0,010", new()), new("old-b2", "b", "+0,010", new())]);
+        Assert.Collection(plan.Operations,
+            value => Assert.Equal(AnnotationOperationKind.Skip, value.Kind),
+            value => Assert.Equal(AnnotationOperationKind.Conflict, value.Kind),
+            value => Assert.Equal(AnnotationOperationKind.Conflict, value.Kind));
+        Assert.Equal("ALREADY_CURRENT", plan.Operations[0].Reasons.Single());
+    }
+
+    [Fact]
+    public void PlansUpdateWhenTheFormattedElevationChanged()
+    {
+        var plan = new ElevationAnnotationPlanner().Build([new ElevationCandidate("a", 13, 0, new(), 0, "PXP", "GOSTC")], [new("old", "a", "+0,010", new())]);
+        Assert.Equal(AnnotationOperationKind.Update, plan.Operations.Single().Kind);
+        Assert.Equal("+0,015", plan.Operations.Single().Text);
+    }
+}