diff --git a/src/AllPlot.cpp b/src/AllPlot.cpp
index 47a3ad0e7..9bb12009e 100644
--- a/src/AllPlot.cpp
+++ b/src/AllPlot.cpp
@@ -297,6 +297,9 @@ AllPlot::AllPlot(AllPlotWindow *parent, Context *context):
     wCurve = new QwtPlotCurve(tr("W' Balance (j)"));
     wCurve->setYAxis(yRight3);
 
+    curveTitle.attach(this);
+    curveTitle.setLabelAlignment(Qt::AlignRight);
+
     intervalHighlighterCurve = new QwtPlotCurve();
     intervalHighlighterCurve->setYAxis(yLeft);
     intervalHighlighterCurve->setData(new IntervalPlotData(this, context));
@@ -1176,6 +1179,10 @@ AllPlot::setDataFromPlot(AllPlot *plot, int startidx, int stopidx)
         stopidx  = plot->timeIndex(plot->timeArray[(stopidx>=plot->timeArray.size()?plot->timeArray.size()-1:stopidx)]/60)-1;
     }
 
+    // center the curve title
+    curveTitle.setYValue(30);
+    curveTitle.setXValue(2);
+
     // make sure indexes are still valid
     if (startidx > stopidx || startidx < 0 || stopidx < 0) return;
 
@@ -1198,6 +1205,14 @@ AllPlot::setDataFromPlot(AllPlot *plot, int startidx, int stopidx)
 
     // attach appropriate curves
     //if (this->legend()) this->legend()->hide();
+    if (showW && parent->wpData->TAU > 0) {
+        QwtText text(QString("tau=%1").arg(parent->wpData->TAU));
+        text.setFont(QFont("Helvetica", 10, QFont::Bold));
+        text.setColor(Qt::red);
+        curveTitle.setLabel(text);
+    } else {
+        curveTitle.setLabel(QwtText(""));
+    }
 
     wCurve->detach();
     wattsCurve->detach();
@@ -1330,6 +1345,7 @@ AllPlot::setDataFromRide(RideItem *_rideItem)
     if (_rideItem == NULL) return;
 
     wattsArray.clear();
+    curveTitle.setLabel(QwtText(QString(""), QwtText::PlainText)); // default to no title
 
     RideFile *ride = rideItem->ride();
     if (ride && ride->dataPoints().size()) {
@@ -1550,6 +1566,14 @@ AllPlot::setShowW(bool show)
 {
     showW = show;
     wCurve->setVisible(show);
+    if (showW && parent->wpData->TAU > 0) {
+        QwtText text(QString("tau=%1").arg(parent->wpData->TAU));
+        text.setFont(QFont("Helvetica", 10, QFont::Bold));
+        text.setColor(Qt::red);
+        curveTitle.setLabel(text);
+    } else {
+        curveTitle.setLabel(QwtText(""));
+    }
     setYMax();
     replot();
 }
diff --git a/src/AllPlot.h b/src/AllPlot.h
index 816eb97e8..85f264ea0 100644
--- a/src/AllPlot.h
+++ b/src/AllPlot.h
@@ -22,6 +22,10 @@
 
 #include <qwt_plot.h>
 #include <qwt_series_data.h>
+#include <qwt_plot_zoomer.h>
+#include <qwt_plot_marker.h>
+#include <qwt_point_3d.h>
+#include <qwt_compat.h>
 #include <QtGui>
 
 class QwtPlotCurve;
@@ -121,6 +125,7 @@ class AllPlot : public QwtPlot
         QwtPlotGrid *grid;
         QVector<QwtPlotMarker*> d_mrk;
         QVector<QwtPlotMarker*> cal_mrk;
+        QwtPlotMarker curveTitle;
         QwtPlotMarker *allMarker1;
         QwtPlotMarker *allMarker2;
         QwtPlotCurve *wattsCurve;
diff --git a/src/WPrime.cpp b/src/WPrime.cpp
index 8b3f0a5d8..fa8b0c36a 100644
--- a/src/WPrime.cpp
+++ b/src/WPrime.cpp
@@ -36,12 +36,9 @@
 #include "WPrime.h"
 
 const double WprimeMultConst = -1.0;
-const double WprimeDecayConst = 336;
 const int WprimeDecayPeriod = 1200; // 1200 seconds or 20 minutes
 const double E = 2.71828183;
 
-inline double decaySchedule(double sec) { return pow(E, -(sec/WprimeDecayConst)); }
-
 WPrime::WPrime()
 {
     // XXX will need to reset metrics when they are added
@@ -64,6 +61,7 @@ WPrime::setRide(RideFile *input)
 
         //XXX will need to reset metrics when they are added
         minY = maxY = 0;
+        TAU=0;
         //qDebug()<<"now work to do"<<time.elapsed();
         return;
     }
@@ -93,13 +91,23 @@ WPrime::setRide(RideFile *input)
     // since we will be running up and down the data series multiple times
     // as we iterate and run a SUMPRODUCT it is best to extract the data
     // into a vector of ints for the watts above CP
+    double totalBelowCP=0;
+    double countBelowCP=0;
     QVector<int> inputArray(last+1);
     for (int i=0; i<last; i++) {
 
         int value = smoothed.value(i);
         inputArray[i] = value > CP ? value-CP : 0;
+
+        if (value < CP) {
+            totalBelowCP += value;
+            countBelowCP++;
+        }
     }
 
+    TAU = 546.00f * pow(E,-0.01*(CP - (totalBelowCP/countBelowCP))) + 316.00f;
+    TAU = int(TAU); // round it down
+
     //qDebug()<<"data preparation took"<<time.elapsed();
 
     // STEP 2: ITERATE OVER DATA TO CREATE W' DATA SERIES
@@ -121,7 +129,7 @@ WPrime::setRide(RideFile *input)
 
         double sumproduct = 0;
         for (int j=0; j<1200 && (i-j) > 0; j++) {
-            sumproduct += inputArray.at(i-j) * pow(E, -(j/WprimeDecayConst)); 
+            sumproduct += inputArray.at(i-j) * pow(E, -(double(j)/TAU)); 
         }
         values[i] = sumproduct * WprimeMultConst;
 
diff --git a/src/WPrime.h b/src/WPrime.h
index 4df5256ba..9289047a7 100644
--- a/src/WPrime.h
+++ b/src/WPrime.h
@@ -45,6 +45,7 @@ class WPrime {
         QVector<double> &xdata() { return xvalues; }
 
         double minY, maxY;
+        double TAU;
 
     private: