Indexer now will now shift discs that virtually but not physically are covering the sensor.
diff --git a/frc971/control_loops/index/index.h b/frc971/control_loops/index/index.h
index 713b050..854b29c 100644
--- a/frc971/control_loops/index/index.h
+++ b/frc971/control_loops/index/index.h
@@ -135,7 +135,8 @@
     // Potentially offsets the position with the knowledge that no discs are
     // currently blocking the top sensor.  This knowledge can be used to move
     // this disc if it is believed to be blocking the top sensor.
-    void ObserveNoTopDiscSensor(double index_position, double index_velocity);
+    // Returns the amount that the disc moved due to this observation.
+    double ObserveNoTopDiscSensor(double index_position, double index_velocity);
 
     // Posedge and negedge disc times.
     ::aos::time::Time bottom_posedge_time_;