diff --git a/src/Nonemm.App/Windows/CheckWindow.axaml.cs b/src/Nonemm.App/Windows/CheckWindow.axaml.cs
index 47685d4..7bf9c87 100644
--- a/src/Nonemm.App/Windows/CheckWindow.axaml.cs
+++ b/src/Nonemm.App/Windows/CheckWindow.axaml.cs
@@ -1,4 +1,4 @@
-using Nonemm.App.Configuration;
+using Nonemm.App.Configuration;
 using Nonemm.App.Theming;
 using Avalonia.Controls;
 using Avalonia.Layout;
@@ -67,25 +67,49 @@ public sealed partial class CheckWindow : RefreshableWindow
     {
         if (session.Check is null)
         {
+            shown.Clear();
             Columns.Children.Clear();
             return;
         }
         IReadOnlyList<CheckColumn> columns = await session.Check.ColumnsAsync();
-        Columns.Children.Clear();
-        Columns.ColumnDefinitions.Clear();
-        foreach (CheckColumn _ in columns)
+        int fontSize = session.Settings.CheckFontSize;
+        // a column is built again only when what it shows is different: most
+        // key presses change one or two of the five
+        if (shown.Count != columns.Count || Columns.Children.Count != columns.Count)
         {
-            Columns.ColumnDefinitions.Add(new ColumnDefinition(GridLength.Star));
+            shown.Clear();
+            Columns.Children.Clear();
+            Columns.ColumnDefinitions.Clear();
+            foreach (CheckColumn _ in columns)
+            {
+                Columns.ColumnDefinitions.Add(new ColumnDefinition(GridLength.Star));
+                shown.Add("");
+                Columns.Children.Add(new Panel());
+            }
         }
-        int at = 0;
-        foreach (CheckColumn column in columns)
+        for (int at = 0; at < columns.Count; at++)
         {
-            Control panel = BuildColumn(column, session.Settings.CheckFontSize);
-            Grid.SetColumn(panel, at++);
-            Columns.Children.Add(panel);
+            string signature = Signature(columns[at], fontSize);
+            if (signature == shown[at])
+            {
+                continue;
+            }
+            shown[at] = signature;
+            Control panel = BuildColumn(columns[at], fontSize);
+            Grid.SetColumn(panel, at);
+            Columns.Children[at] = panel;
         }
     }
 
+    /// What the column shows, as text.
+    private readonly List<string> shown = [];
+
+    private static string Signature(CheckColumn column, int fontSize) =>
+        $"{fontSize}|{column.Source}|{column.Held}|" + string.Join(
+            ';',
+            column.Candidates.Select(c =>
+                $"{c.Text}:{c.Quality}:{c.Verdict?.IsDupe}:{c.Verdict?.Points}:{c.Verdict?.NewMultipliers.Count}"));
+
     private static Control BuildColumn(CheckColumn column, int fontSize)
     {
         StackPanel panel = new() { Margin = new Avalonia.Thickness(0, 0, 8, 0) };
diff --git a/src/Nonemm.Contests/ContestLog.cs b/src/Nonemm.Contests/ContestLog.cs
index 741f2c2..5596d00 100644
--- a/src/Nonemm.Contests/ContestLog.cs
+++ b/src/Nonemm.Contests/ContestLog.cs
@@ -50,6 +50,10 @@ public sealed class ContestLog
 
     public Contest Contest => contest;
 
+    /// Goes up with every change to the contacts, so something worked out
+    /// from the log can be kept until this changes.
+    public int Revision { get; private set; }
+
     public IReadOnlyList<Qso> Qsos => qsos;
 
     /// The contacts alone. In WAE the log also holds QTC traffic, and a QTC
@@ -123,6 +127,7 @@ public sealed class ContestLog
             Qso scored = ApplyVerdict(qso, verdict);
             qsos.Add(scored);
             Index(scored, verdict);
+            Revision++;
             return scored;
         }
     }
@@ -342,6 +347,7 @@ public sealed class ContestLog
 
     private void Rebuild()
     {
+        Revision++;
         workedKeys.Clear();
         trafficWith.Clear();
         claimedMultipliers.Clear();
diff --git a/src/Nonemm.Session/CheckWindowSources.cs b/src/Nonemm.Session/CheckWindowSources.cs
index 306c586..7762fe1 100644
--- a/src/Nonemm.Session/CheckWindowSources.cs
+++ b/src/Nonemm.Session/CheckWindowSources.cs
@@ -145,15 +145,50 @@ public sealed class CheckWindowSources
         new(match.Call, match.Quality, session.JudgeCall(match.Call));
 
 
-    private IReadOnlyList<string> LoggedCalls() =>
-        session.Log.Qsos.Select(q => q.Call.Text).Distinct(StringComparer.Ordinal).ToList();
+    // The three lists below are asked for on every key press and change far
+    // less often, so each is kept until what it is made from changes.
+    private int loggedRevision = -1;
+    private IReadOnlyList<string> logged = [];
+    private CallHistory? historyOf;
+    private IReadOnlyList<string> history = [];
+    private IReadOnlyList<Spot>? spottedOf;
+    private IReadOnlyList<string> spotted = [];
 
-    private IReadOnlyList<string> HistoryCalls() => [.. session.Session.History.Calls];
+    private IReadOnlyList<string> LoggedCalls()
+    {
+        int revision = session.Log.Revision;
+        if (revision != loggedRevision)
+        {
+            logged = session.Log.Qsos.Select(q => q.Call.Text).Distinct(StringComparer.Ordinal).ToList();
+            loggedRevision = revision;
+        }
+        return logged;
+    }
 
-    private IReadOnlyList<string> SpottedCalls() =>
-        bandmap.All()
-            .Where(s => s.IsStation)
-            .Select(s => s.Call.Text)
-            .Distinct(StringComparer.Ordinal)
-            .ToList();
+    private IReadOnlyList<string> HistoryCalls()
+    {
+        CallHistory current = session.Session.History;
+        if (!ReferenceEquals(current, historyOf))
+        {
+            history = [.. current.Calls];
+            historyOf = current;
+        }
+        return history;
+    }
+
+    private IReadOnlyList<string> SpottedCalls()
+    {
+        // the bandmap hands out the same list until its spots change
+        IReadOnlyList<Spot> all = bandmap.All();
+        if (!ReferenceEquals(all, spottedOf))
+        {
+            spotted = all
+                .Where(s => s.IsStation)
+                .Select(s => s.Call.Text)
+                .Distinct(StringComparer.Ordinal)
+                .ToList();
+            spottedOf = all;
+        }
+        return spotted;
+    }
 }