diff --git a/src/main/java/beastlabs/prevalence/PrevalenceList.java b/src/main/java/beastlabs/prevalence/PrevalenceList.java
index 163324d..90c537b 100644
--- a/src/main/java/beastlabs/prevalence/PrevalenceList.java
+++ b/src/main/java/beastlabs/prevalence/PrevalenceList.java
@@ -294,20 +294,35 @@ public void fromXML(Node node) {
 
 	@Override
 	/** scale only those items associated with a node and leave the rest **/
-	public int scale(double fScale) {
+	public double scale(double fScale) {
 		Set<Integer> nodes = m_nodeIDtoItemMap.keySet();
 		for (Integer nNodeID : nodes) {
 			int iTime = indexOfNode(nNodeID);
-			Item item = m_items.get(iTime); 
+			Item item = m_items.get(iTime);
 			move(iTime, item.m_fTime * fScale);
 		}
-		return nodes.size();
+		return nodes.size() * Math.log(fScale);
+	}
+
+	/**
+	 * Read this list's position on its dilation axis: sum of times across all
+	 * items associated with a node. Each such time is multiplied by the scale
+	 * factor in {@link #scale(double)}, so the sum is exactly {@code s}-equivariant.
+	 */
+	@Override
+	public double getScalableValue() {
+		double sum = 0.0;
+		for (Integer nNodeID : m_nodeIDtoItemMap.keySet()) {
+			int iTime = indexOfNode(nNodeID);
+			sum += m_items.get(iTime).m_fTime;
+		}
+		return sum;
 	}
 
 	@Override
 	public void scaleOne(int i, double scale) {
 		int iTime = indexOfNode(i);
-		Item item = m_items.get(iTime); 
+		Item item = m_items.get(iTime);
 		move(iTime, item.m_fTime * scale);
 	}
 
diff --git a/src/main/java/beastlabs/prevalence/TreeScaleOperator.java b/src/main/java/beastlabs/prevalence/TreeScaleOperator.java
index b13abfc..8a2e381 100644
--- a/src/main/java/beastlabs/prevalence/TreeScaleOperator.java
+++ b/src/main/java/beastlabs/prevalence/TreeScaleOperator.java
@@ -59,16 +59,18 @@ public double proposal() {
 	        double d = Randomizer.nextDouble();
 	        double scale = (m_fScaleFactor + (d * ((1.0 / m_fScaleFactor) - m_fScaleFactor)));
 	        
-	    	Tree tree = m_tree.get(); 
+	    	Tree tree = m_tree.get();
 	        // scale the beast.tree
-	    	int nInternalNodes = tree.scale(scale);
+	        // tree.scale returns the log Jacobian (dof * log(scale));
+	        // operator adds the -2*log(scale) kernel-symmetry correction.
+	    	final double treeLogJacobian = tree.scale(scale);
 
 	    	PrevalenceList list = m_list.get();
-	    	// scale only internal nodes in the list
-	    	// nNodesScaled is the number of nodes that have been scaled
-	    	int nNodesScaled = list.scale(scale);
+	    	// scale only internal nodes in the list (return discarded —
+	    	// see TODO below; list's contribution to HR is not currently included)
+	    	list.scale(scale);
 	        // TODO: check the HastingsRatio, since the prevalence list is assumed to be unchanged here
-	        return Math.log(scale) * (nInternalNodes - 2);
+	        return treeLogJacobian - 2 * Math.log(scale);
     	} catch (Exception e) {
 			return Double.NEGATIVE_INFINITY;
 		}