diff --git a/libraries/AP_Soaring/Variometer.cpp b/libraries/AP_Soaring/Variometer.cpp
index 3cf266c61c..8e76a78e98 100644
--- a/libraries/AP_Soaring/Variometer.cpp
+++ b/libraries/AP_Soaring/Variometer.cpp
@@ -31,7 +31,7 @@ void Variometer::update(const float polar_K, const float polar_Cd0, const float
     _aspd_filt_constrained = _aspd_filt>minV ? _aspd_filt : minV;
 
 
-    float tau = calculate_circling_time_constant();
+    tau = calculate_circling_time_constant();
 
     float dt = (float)(AP_HAL::micros64() - _prev_update_time)/1e6;
 
diff --git a/libraries/AP_Soaring/Variometer.h b/libraries/AP_Soaring/Variometer.h
index 46c994d458..56be8dfde7 100644
--- a/libraries/AP_Soaring/Variometer.h
+++ b/libraries/AP_Soaring/Variometer.h
@@ -50,6 +50,7 @@ public:
     float displayed_reading;
     float raw_climb_rate;
     float smoothed_climb_rate;
+    float tau;
 
     void update(const float polar_K, const float polar_CD0, const float polar_B);
     float calculate_aircraft_sinkrate(float phi, const float polar_K, const float polar_CD0, const float polar_B);