diff --git a/cpp/Errors.cpp b/cpp/Errors.cpp
index d75da2b2d..af76b5d49 100644
--- a/cpp/Errors.cpp
+++ b/cpp/Errors.cpp
@@ -6,6 +6,7 @@
  * @author  Christian Potthast
  */
 
+#include <boost/bind.hpp>
 #include <boost/foreach.hpp>
 #include "Errors.h"
 
@@ -30,8 +31,21 @@ struct equalsVector : public std::binary_function<const Vector&, const Vector&,
 };
 
 bool Errors::equals(const Errors& expected, double tol) const {
-  if( size() != expected.size() ) return false;
-  return equal(begin(),end(),expected.begin(),equalsVector(tol));
+	if( size() != expected.size() ) return false;
+	return equal(begin(),end(),expected.begin(),equalsVector(tol));
+	// TODO: use boost::bind(&equal_with_abs_tol,_1, _2,tol)
+}
+
+/* ************************************************************************* */
+Errors Errors::operator-(const Errors& b) const {
+	size_t m = size();
+  if (b.size()!=m)
+    throw(std::invalid_argument("Errors::operator-: incompatible sizes"));
+	Errors result;
+	Errors::const_iterator it = b.begin();
+  BOOST_FOREACH(const Vector& ai, *this)
+		result.push_back(ai - *(it++));
+	return result;
 }
 
 /* ************************************************************************* */
diff --git a/cpp/Errors.h b/cpp/Errors.h
index deb100da7..37fe49dcf 100644
--- a/cpp/Errors.h
+++ b/cpp/Errors.h
@@ -26,6 +26,9 @@ namespace gtsam {
     /** equals, for unit testing */
     bool equals(const Errors& expected, double tol=1e-9) const;
 
+    /** subtraction */
+    Errors operator-(const Errors& b) const;
+
   }; // Errors
 
   /**