diff --git a/rowers/interactiveplots.py b/rowers/interactiveplots.py
index 7fe3049e..e1a1f0eb 100644
--- a/rowers/interactiveplots.py
+++ b/rowers/interactiveplots.py
@@ -176,20 +176,24 @@ def interactive_hr_piechart(df,rower,title):
         return "","Not enough data to make a chart"
 
     df.sort_values(by='hr',inplace=True)
+    df['timehr'] = df['deltat']*df['hr']
+
+    sumtimehr = df['deltat'].sum()
+
     qry = 'hr < {ut2}'.format(ut2=rower.ut2)
-    frac_lut2 = len(df.query(qry))/len(df)
+    frac_lut2 = df.query(qry)['deltat'].sum()/sumtimehr
 
     qry = 'hr < {ut1}'.format(ut1=rower.ut1,ut2=rower.ut2)
-    frac_ut2 = len(df.query(qry))/len(df)
+    frac_ut2 = df.query(qry)['deltat'].sum()/sumtimehr
 
     qry = 'hr < {at}'.format(ut1=rower.ut1,at=rower.at)
-    frac_ut1 = len(df.query(qry))/len(df)
+    frac_ut1 = df.query(qry)['deltat'].sum()/sumtimehr
 
     qry = 'hr < {tr}'.format(at=rower.at,tr=rower.tr)
-    frac_at = len(df.query(qry))/len(df)
+    frac_at = df.query(qry)['deltat'].sum()/sumtimehr
 
     qry = 'hr < {an}'.format(tr=rower.tr,an=rower.an)
-    frac_tr = len(df.query(qry))/len(df)
+    frac_tr = df.query(qry)['deltat'].sum()/sumtimehr
 
     frac_an = 1.