diff --git a/GTSAM-Concepts.md b/GTSAM-Concepts.md
index fca273c77..4acc24d73 100644
--- a/GTSAM-Concepts.md
+++ b/GTSAM-Concepts.md
@@ -27,6 +27,7 @@ In detail, we ask the following are defined in the namespace `gtsam::manifold::t
 * types: 
     * `TangentVector`, type that lives in tangent space. This will almost always be an `Eigen::Matrix<double,n,1>`.
 	* `DefaultChart`,  the default chart at a point p
+	* `ChartJacobian`, a typedef for `OptionalJacobian<dimension<Manifold>::value, dimension<Manifold>::value>`.  
 * valid expressions:
     * `size_t dim = getDimension(p);` free function should be defined in case the dimension is not known at compile time.
 
@@ -34,11 +35,10 @@ Anything else?
 
 Chart
 -----
-A given chart is implemented using a small class that defines the chart itself (from manifold to tangent space) and its inverse.
+A given chart is implemented using a small class that defines the chart itself (from manifold to tangent space) and its inverse. The trait `gtsam::manifold::traits::DefaultChart<ManifoldType>::type` should point to the chart implementation. This specialization requires the following:
 
 * types:
     * `ManifoldType`, a pointer back to the type
-    * `Jacobian`, a typedef for `gtsam::OptionalJacobian<Dimension, Dimension>` where the dimension is taken from `gtsam::maifold::traits::dimension`.
 * valid expressions: 
     * `v = Chart::Local(p,q,Hp,Hq)`, the chart, from manifold to tangent space, think of it as *q (-) p*
     * `p = Chart::Retract(p,v,Hp,Hv)`, the inverse chart, from tangent space to manifold, think of it as *p (+) v*
diff --git a/gtsam/base/concepts.h b/gtsam/base/concepts.h
index 7608c0776..7c8fa3543 100644
--- a/gtsam/base/concepts.h
+++ b/gtsam/base/concepts.h
@@ -54,9 +54,12 @@ namespace traits {
 template<typename Manifold> struct dimension;
 template<typename Manifold> struct TangentVector;
 template<typename Manifold> struct DefaultChart;
+template<typename Manifold> struct ChartJacobian {
+  typedef OptionalJacobian<dimension<Manifold>::value, dimension<Manifold>::value> value;
+};
 //@}
 
-}// \ namespace traits
+}// \ namespace manifold::traits
 
 /// Check invariants for Manifold type
 template<typename T>