diff --git a/lib/average.h b/lib/average.h
index 4649eb79df..d491b533ab 100644
--- a/lib/average.h
+++ b/lib/average.h
@@ -18,41 +18,62 @@
 
 struct AVERAGE {
     double n;       // double to avoid integer overflow
+    double weight;
+        // if n < MIN_SAMPLES, sum of weights
+        // else recent average weight
     double mean;
-    double sum_var;
-        // sample variance is this divided by (n-1)
-    double recent_mean;
-    double recent_var;
+        // if n < MIN_SAMPLES, weighted sum of samples
+        // else recent average
+    double var;
+        // if n < MIN_SAMPLES, weighted sum of vars
+        // else recent var
 
-    void update(double sample) {
+    void update(double sample, double w) {
+        double delta;
         if (sample < 0) return;
         if (n > MIN_SAMPLES) {
-            if (sample > recent_mean*SAMPLE_LIMIT) {
-                sample = recent_mean*SAMPLE_LIMIT;
+            if (sample > mean*SAMPLE_LIMIT) {
+                sample = mean*SAMPLE_LIMIT;
             }
         }
         n++;
-        double delta = sample - mean;
-        mean += delta/n;
-        sum_var += delta*(sample-mean);
 
         if (n < MIN_SAMPLES) {
-            recent_mean = mean;
-            recent_var = sum_var/n;
+            weight += w;
+            mean += w*sample;
+            delta = (sample - mean/weight);
+            var += delta*delta*w;
+        } else if (n == MIN_SAMPLES) {
+            mean /= weight;
+            var /= weight;
+            weight /= n;
         } else {
             // update recent averages
-            delta = sample - recent_mean;
-            recent_mean += SAMPLE_WEIGHT*delta;
-            double d2 = delta*delta - recent_var;
-            recent_var += SAMPLE_WEIGHT*d2;
+            if (w > weight*10) w = weight*10;
+            double rel_weight = w/weight;
+            double sample_weight = SAMPLE_WEIGHT * rel_weight;
+
+            delta = sample - mean;
+            mean += sample_weight*delta;
+
+            double d2 = delta*delta - var;
+            var += sample_weight*d2;
+
+            weight += SAMPLE_WEIGHT*(w - weight);
+        }
+    }
+    double get_mean() {
+        if (n < MIN_SAMPLES) {
+            return mean/weight;
+        } else {
+            return mean;
         }
     }
 
     void clear() {
         n = 0;
+        weight = 0;
         mean = 0;
-        sum_var = 0;
-        recent_mean = 0;
-        recent_var = 0;
+        var = 0;
     }
 };