diff --git a/frc971/constants.h b/frc971/constants.h
index fe47418..0b6b725 100644
--- a/frc971/constants.h
+++ b/frc971/constants.h
@@ -111,6 +111,10 @@
 
     // How high the elevator has to be before we start zeroing the arm.
     double arm_zeroing_height;
+
+    // The length of the arm, from the axis of the bottom pivot to the axis of
+    // the top pivot.
+    double arm_length;
   };
   Fridge fridge;