diff --git a/js/atree.js b/js/atree.js
index dcc060e..055bbbb 100644
--- a/js/atree.js
+++ b/js/atree.js
@@ -125,16 +125,16 @@ const default_abils = {
 /**
  * Update ability tree internal representation. (topologically sorted node list)
  *
- * Signature: AbilityTreeUpdateNode(build: Build) => ATree (List of atree nodes in topological order)
+ * Signature: AbilityTreeUpdateNode(player-class: str) => ATree (List of atree nodes in topological order)
  */
 const atree_node = new (class extends ComputeNode {
     constructor() { super('builder-atree-update'); }
 
     compute_func(input_map) {
-        if (input_map.size !== 1) { throw "AbilityTreeUpdateNode accepts exactly one input (build)"; }
-        const [build] = input_map.values();  // Extract values, pattern match it into size one list and bind to first element
+        if (input_map.size !== 1) { throw "AbilityTreeUpdateNode accepts exactly one input (player-class)"; }
+        const [player_class] = input_map.values();  // Extract values, pattern match it into size one list and bind to first element
 
-        const atree_raw = atrees[wep_to_class.get(build.weapon.statMap.get('type'))];
+        const atree_raw = atrees[player_class];
         if (!atree_raw) return null;
 
         let atree_map = new Map();
diff --git a/js/builder_graph.js b/js/builder_graph.js
index 28140fe..cff072a 100644
--- a/js/builder_graph.js
+++ b/js/builder_graph.js
@@ -435,6 +435,17 @@ class BuildAssembleNode extends ComputeNode {
     }
 }
 
+class PlayerClassNode extends ValueCheckComputeNode {
+    constructor(name) { super(name); }
+
+    compute_func(input_map) {
+        if (input_map.size !== 1) { throw "PlayerClassNode accepts exactly one input (build)"; }
+        const [build] = input_map.values();  // Extract values, pattern match it into size one list and bind to first element
+
+        return wep_to_class.get(build.weapon.statMap.get('type'));
+    }
+}
+
 /**
  * Read an input field and parse into a list of powderings.
  * Every two characters makes one powder. If parsing fails, NULL is returned.
@@ -1085,8 +1096,9 @@ function builder_graph_init() {
 
     // Phase 3/3: Set up atree stuff.
 
+    let class_node = new PlayerClassNode('builder-class').link_to(build_node);
     // These two are defined in `atree.js`
-    atree_node.link_to(build_node, 'build');
+    atree_node.link_to(class_node, 'player-class');
     atree_merge.link_to(build_node, 'build');
     atree_graph_creator = new AbilityTreeEnsureNodesNode(build_node, stat_agg_node)
                                     .link_to(atree_collect_spells, 'spells');
diff --git a/js/computation_graph.js b/js/computation_graph.js
index d0d5b7a..bf45564 100644
--- a/js/computation_graph.js
+++ b/js/computation_graph.js
@@ -14,7 +14,10 @@ class ComputeNode {
         this.name = name;
         this.update_task = null;
         this.fail_cb = false;   // Set to true to force updates even if parent failed.
-        this.dirty = true;
+        this.dirty = 2;         // 3 states:
+                                // 2: dirty
+                                // 1: possibly dirty
+                                // 0: clean
         this.inputs_dirty = new Map();
         this.inputs_dirty_count = 0;
         all_nodes.push(this);
@@ -27,15 +30,17 @@ class ComputeNode {
         if (this.inputs_dirty_count != 0) {
             return;
         }
-        if (!this.dirty) {
+        if (this.dirty === 0) {
             return;
         }
-        let calc_inputs = new Map();
-        for (const input of this.inputs) {
-            calc_inputs.set(this.input_translation.get(input.name), input.value);
+        if (this.dirty == 2) {
+            let calc_inputs = new Map();
+            for (const input of this.inputs) {
+                calc_inputs.set(this.input_translation.get(input.name), input.value);
+            }
+            this.value = this.compute_func(calc_inputs);
         }
-        this.value = this.compute_func(calc_inputs);
-        this.dirty = false;
+        this.dirty = 0;
         for (const child of this.children) {
             child.mark_input_clean(this.name, this.value);
         }
@@ -64,12 +69,12 @@ class ComputeNode {
         }
     }
 
-    mark_dirty() {
-        if (!this.dirty) {
-            this.dirty = true;
+    mark_dirty(dirty_state=2) {
+        if (this.dirty < dirty_state) {
+            this.dirty = dirty_state;
             for (const child of this.children) {
                 child.mark_input_dirty(this.name);
-                child.mark_dirty();
+                child.mark_dirty(dirty_state);
             }
         }
         return this;
@@ -125,6 +130,50 @@ class ComputeNode {
     }
 }
 
+class ValueCheckComputeNode extends ComputeNode {
+    constructor(name) { super(name); }
+
+    /**
+     * Request update of this compute node. Pushes updates to children,
+     * but only if this node's value changed.
+     */
+    update() {
+        if (this.inputs_dirty_count != 0) {
+            return;
+        }
+        if (this.dirty === 0) {
+            return;
+        }
+
+        let calc_inputs = new Map();
+        for (const input of this.inputs) {
+            calc_inputs.set(this.input_translation.get(input.name), input.value);
+        }
+        let val = this.compute_func(calc_inputs);
+        if (val !== this.value) {
+            this.mark_dirty(2);
+        }
+        else {
+            console.log("soft update");
+        }
+        this.value = val;
+
+        this.dirty = 0;
+        for (const child of this.children) {
+            child.mark_input_clean(this.name, this.value);
+        }
+        return this;
+    }
+
+    /**
+     * Defaulting to "dusty" state.
+     */
+    mark_dirty(dirty_state="unused") {
+        return super.mark_dirty(1);
+    }
+
+}
+
 /**
  * Schedule a ComputeNode to be updated.
  *