diff --git a/Kernel/src/renderive/real_time_data/History_Real_Time_Data.hpp b/Kernel/src/renderive/real_time_data/History_Real_Time_Data.hpp
index 99867f3..6f28d1a 100644
--- a/Kernel/src/renderive/real_time_data/History_Real_Time_Data.hpp
+++ b/Kernel/src/renderive/real_time_data/History_Real_Time_Data.hpp
@@ -31,7 +31,12 @@ public:
     void update(Value value, std::size_t retain_latest_count);
     void clear();
     std::size_t retain_latest(std::size_t count);
+    struct Snapshot {
+        Container values;
+        Real_Time_Data_Update_State update_state;
+    };
     Container snapshot() const;
+    Snapshot snapshot_with_update_state() const;
     std::size_t size() const;
     std::uint64_t revision() const;
     Real_Time_Data_Retention retention() const noexcept override;
@@ -49,6 +54,7 @@ private:
     void reserve_update_times(std::size_t capacity);
     void publish_render_state() override;
     const Container& render_state_value() const noexcept;
+    const Real_Time_Data_Update_State& render_update_state_value() const noexcept;
     mutable Mutex mutex_;
     std::recursive_mutex mutation_mutex_;
     Observer observer_;
@@ -61,7 +67,7 @@ private:
     std::size_t update_times_size_{};
     std::size_t update_times_capacity_{};
     std::uint64_t revision_{};
-    std::uint64_t render_revision_{};
+    Real_Time_Data_Update_State render_update_state_{};
     std::uint64_t total_update_count_{};
     std::uint64_t last_update_time_ns_{};
 };
diff --git a/Kernel/src/renderive/real_time_data/History_Real_Time_Data.inl b/Kernel/src/renderive/real_time_data/History_Real_Time_Data.inl
index 179b2b0..7936238 100644
--- a/Kernel/src/renderive/real_time_data/History_Real_Time_Data.inl
+++ b/Kernel/src/renderive/real_time_data/History_Real_Time_Data.inl
@@ -101,6 +101,15 @@ auto History_Real_Time_Data<Value_Type, Container, Mutex, Observer>::snapshot()
     return *cache_state_;
 }
 template <class Value_Type, class Container, Mutex_Type Mutex, class Observer>
+auto History_Real_Time_Data<Value_Type, Container, Mutex, Observer>::snapshot_with_update_state() const -> Snapshot {
+    std::lock_guard < Mutex > lock(mutex_);
+    const Real_Time_Data_Update_State update_state{
+        this, Real_Time_Data_Retention::history, revision_, last_update_time_ns_,
+        total_update_count_, cache_state_->size()
+    };
+    return {*cache_state_, update_state};
+}
+template <class Value_Type, class Container, Mutex_Type Mutex, class Observer>
 std::size_t History_Real_Time_Data<Value_Type, Container, Mutex, Observer>::size() const {
     std::lock_guard < Mutex > lock(mutex_);
     return cache_state_->size();
@@ -144,12 +153,20 @@ std::size_t History_Real_Time_Data<Value_Type, Container, Mutex, Observer>::disc
 template <class Value_Type, class Container, Mutex_Type Mutex, class Observer>
 void History_Real_Time_Data<Value_Type, Container, Mutex, Observer>::publish_render_state() {
     std::lock_guard < Mutex > lock(mutex_);
-    if (render_revision_ == revision_) return;
+    if (render_update_state_.revision == revision_) return;
     *scratch_state_ = *cache_state_;
     std::swap(render_state_, scratch_state_);
-    render_revision_ = revision_;
+    render_update_state_ = {
+        this, Real_Time_Data_Retention::history, revision_, last_update_time_ns_,
+        total_update_count_, render_state_->size()
+    };
 }
 template <class Value_Type, class Container, Mutex_Type Mutex, class Observer>
 auto History_Real_Time_Data<Value_Type, Container, Mutex, Observer>::render_state_value() const noexcept -> const Container& {
     return *render_state_;
 }
+template <class Value_Type, class Container, Mutex_Type Mutex, class Observer>
+auto History_Real_Time_Data<Value_Type, Container, Mutex, Observer>::render_update_state_value() const noexcept
+    -> const Real_Time_Data_Update_State& {
+    return render_update_state_;
+}
diff --git a/Kernel/src/renderive/state/Render_State_View.hpp b/Kernel/src/renderive/state/Render_State_View.hpp
index f01a54e..a35324c 100644
--- a/Kernel/src/renderive/state/Render_State_View.hpp
+++ b/Kernel/src/renderive/state/Render_State_View.hpp
@@ -7,6 +7,10 @@ public:
     [[nodiscard]] const auto& get(const Source& source) const noexcept {
         return source.render_state_value();
     }
+    template <class Source>
+    [[nodiscard]] const auto& update_state(const Source& source) const noexcept {
+        return source.render_update_state_value();
+    }
 private:
     friend class Renderable_Base;
     friend class Frame_Render_Snapshot;
diff --git a/render_2D/render_2D/plottable/Sweep_Spectrum.cpp b/render_2D/render_2D/plottable/Sweep_Spectrum.cpp
index 3c4309d..a3632f8 100644
--- a/render_2D/render_2D/plottable/Sweep_Spectrum.cpp
+++ b/render_2D/render_2D/plottable/Sweep_Spectrum.cpp
@@ -3,18 +3,37 @@
 #include "Plottable_Real_Time_Data.h"
 #include "../render/Blend2D_Cache.h"
 #include "../renderable/Renderable_p.h"
-#include <algorithm>
-#include <cmath>
+#include <cstdint>
 #include <deque>
 #include <optional>
 namespace renderive::detail {
 namespace {
 using Sweep_Spectrum_History = Plottable_History_Real_Time_Data<std::vector<double>, std::deque<std::vector<double>>>;
-std::vector<double> flatten(const std::deque<std::vector<double>>& blocks) {
+std::size_t current_sweep_block_count(std::uint64_t total_update_count,
+                                      std::size_t block_count) {
+    if (total_update_count == 0) return 0;
+    return static_cast<std::size_t>((total_update_count - 1) % block_count) + 1;
+}
+std::vector<double> flatten_latest(const std::deque<std::vector<double>>& blocks,
+                                   std::size_t block_count) {
     std::vector<double> values;
-    for (const auto& block : blocks) values.insert(values.end(), block.begin(), block.end());
+    const std::size_t first = blocks.size() - block_count;
+    std::size_t value_count{};
+    for (std::size_t index = first; index < blocks.size(); ++index) {
+        value_count += blocks[index].size();
+    }
+    values.reserve(value_count);
+    for (std::size_t index = first; index < blocks.size(); ++index) {
+        values.insert(values.end(), blocks[index].begin(), blocks[index].end());
+    }
     return values;
 }
+Range completed_frequency_range(Range frequency_range,
+                                std::size_t completed_block_count,
+                                std::size_t block_count) {
+    const double completed = static_cast<double>(completed_block_count) / static_cast<double>(block_count);
+    return {frequency_range.origin, frequency_range.origin + frequency_range.length() * completed};
+}
 }
 struct Sweep_Spectrum::Impl
 : Base::next_Impl<Impl> {
@@ -71,8 +90,17 @@ std::size_t Sweep_Spectrum::stored_point_count() const {
 }
 std::size_t Sweep_Spectrum::rendered_point_count() const {
     const auto state = Renderable::state<State>();
-    const auto values = flatten(d_func<Impl>().blocks->snapshot());
-    return curve_points(values, state.frequency_range, d_func<Impl>().frequency_axis->transform(), d_func<Impl>().power_axis->transform(), state.visible_range_only, state.interpolation_mode).size();
+    const auto snapshot = d_func<Impl>().blocks->snapshot_with_update_state();
+    const std::size_t block_count = static_cast<std::size_t>(state.block_count.get());
+    const std::size_t completed_block_count =
+        current_sweep_block_count(snapshot.update_state.total_update_count, block_count);
+    const auto values = flatten_latest(snapshot.values, completed_block_count);
+    const Range frequency_range = completed_frequency_range(
+        state.frequency_range, completed_block_count, block_count);
+    return curve_points(values, frequency_range,
+                        d_func<Impl>().frequency_axis->transform(),
+                        d_func<Impl>().power_axis->transform(),
+                        state.visible_range_only, state.interpolation_mode).size();
 }
 Sweep_Spectrum::Observer Sweep_Spectrum::capture_observation() const {
     const auto value = Renderable::published_state<State>();
@@ -88,16 +116,21 @@ void Sweep_Spectrum::Impl::prepare_frame(const Prepare_Render_Context& context)
     const auto& view = context.frame.render_state;
     const auto& state = control.render_state<State>(view);
     const auto& published_blocks = view.get(*blocks);
-    const auto values = flatten(published_blocks);
+    const auto& published_update_state = view.update_state(*blocks);
+    const std::size_t block_count = static_cast<std::size_t>(state.block_count.get());
+    const std::size_t completed_block_count = current_sweep_block_count(
+        published_update_state.total_update_count, block_count);
+    const auto values = flatten_latest(published_blocks, completed_block_count);
     auto& output = prepare_buffer;
     output = {};
     if (values.size() < 2) return;
     const Axis_Transform x = frequency_axis->transform(view);
     const Axis_Transform y = power_axis->transform(view);
-    output.points = curve_points(values, state.frequency_range, x, y,
+    const Range frequency_range = completed_frequency_range(
+        state.frequency_range, completed_block_count, block_count);
+    output.points = curve_points(values, frequency_range, x, y,
                                  state.visible_range_only, state.interpolation_mode);
-    const double completed = std::min(1.0, static_cast<double>(published_blocks.size()) / state.block_count.get());
-    const double frequency = state.frequency_range.origin + state.frequency_range.length() * completed;
+    const double frequency = frequency_range.target;
     output.current_first = mapped_point(x, frequency, y, y.coordinate_range.origin);
     output.current_second = mapped_point(x, frequency, y, y.coordinate_range.target);
     output.valid = true;
diff --git a/web_server/app/render_2D/Gallery_Scene2D.cpp b/web_server/app/render_2D/Gallery_Scene2D.cpp
index 8a6a30f..67f7e3a 100644
--- a/web_server/app/render_2D/Gallery_Scene2D.cpp
+++ b/web_server/app/render_2D/Gallery_Scene2D.cpp
@@ -19,6 +19,7 @@
 #include <chrono>
 #include <cmath>
 #include <memory>
+#include <numbers>
 #include <span>
 #include <string>
 #include <vector>
@@ -35,6 +36,8 @@ struct Observer_Pfr_Adapter<Render_Scene_2D::Observer> {
         Render_Scene_2D::Observer, Render_Scene_2D::Observer_Fields>;
 };
 namespace {
+constexpr std::size_t sweep_bins_per_block = 64;
+constexpr std::size_t sweep_block_count = 8;
 std::shared_ptr<Frame_Control_Strategy_Base> make_strategy(
     Gallery_Frame_Mode mode) {
     switch (mode) {
@@ -349,8 +352,8 @@ private:
         } else if (case_id_ == "sweep_spectrum") {
             Sweep_Spectrum::State state;
             state.frequency_range = {0.0, 300.0};
-            state.bins_per_block = 64;
-            state.block_count = 8;
+            state.bins_per_block = static_cast<int>(sweep_bins_per_block);
+            state.block_count = static_cast<int>(sweep_block_count);
             Sweep_Spectrum::Builder builder{state, &attach};
             sweep_ = build<Sweep_Spectrum>(
                 builder, root, domain_axis_, value_axis_);
@@ -382,9 +385,16 @@ private:
     }
 
     void update_samples() {
-        const std::size_t count = waterfall_ ? 256U : afterglow_ ? 192U : 512U;
+        const std::size_t count =
+            waterfall_ ? 256U :
+            afterglow_ ? 192U :
+            sweep_ ? sweep_bins_per_block * sweep_block_count : 512U;
         std::vector<double> values(count);
-        const double time = static_cast<double>(sample_sequence_++) * 0.075;
+        const std::uint64_t sample_sequence = sample_sequence_++;
+        const std::uint64_t time_sequence = sweep_
+                                                ? sample_sequence / sweep_block_count * sweep_block_count
+                                                : sample_sequence;
+        const double time = static_cast<double>(time_sequence) * 0.075;
         for (std::size_t index = 0; index < count; ++index) {
             const double x = static_cast<double>(index) / (count - 1);
             const auto gaussian = [](double value, double center, double width) {
@@ -402,15 +412,26 @@ private:
         if (waterfall_) waterfall_->append_row(current_time_of_day(), values);
         if (afterglow_) afterglow_->append_spectrum(values);
         if (sweep_) {
-            values.resize(64);
-            sweep_->append_block(values);
+            const std::size_t block_index = static_cast<std::size_t>(
+                sample_sequence % sweep_block_count);
+            const std::size_t first = block_index * sweep_bins_per_block;
+            sweep_->append_block(std::span<const double>(
+                values.data() + first, sweep_bins_per_block));
         }
         if (trace_) trace_->append_sample(current_time_of_day(), std::sin(time));
         if (constellation_) {
-            const double phase = time * 1.7;
+            constexpr std::size_t symbol_count =
+                static_cast<std::size_t>(Constellation_Diagram_Type::Psk8);
+            const std::size_t symbol_index = sample_sequence % symbol_count;
+            const double phase = 2.0 * std::numbers::pi *
+                                 static_cast<double>(symbol_index) /
+                                 static_cast<double>(symbol_count);
+            const double i_noise =
+                std::sin(time * 17.0 + static_cast<double>(symbol_index) * 0.73) * 0.04;
+            const double q_noise =
+                std::cos(time * 19.0 + static_cast<double>(symbol_index) * 1.11) * 0.04;
             constellation_->append_point(
-                {std::cos(phase) + std::sin(time * 9.0) * 0.08,
-                 std::sin(phase) + std::cos(time * 7.0) * 0.08});
+                {std::cos(phase) + i_noise, std::sin(phase) + q_noise});
         }
     }