Calibrated camera offset.

Change-Id: I10113c9b80695c0b2407cd1df6fd3fe40d6390ca
diff --git a/y2017/constants.h b/y2017/constants.h
index 829af88..1d6eede 100644
--- a/y2017/constants.h
+++ b/y2017/constants.h
@@ -123,6 +123,8 @@
 
   double down_error;
   const char *vision_name;
+
+  double vision_error;
 };
 
 // Creates (once) a Values instance for ::aos::network::GetTeamNumber() and