diff --git a/Grid/lattice/Lattice.h b/Grid/lattice/Lattice.h
index 9f5f1da7..c4adf86a 100644
--- a/Grid/lattice/Lattice.h
+++ b/Grid/lattice/Lattice.h
@@ -46,3 +46,4 @@ Author: Peter Boyle <paboyle@ph.ed.ac.uk>
 #include <Grid/lattice/Lattice_unary.h>
 #include <Grid/lattice/Lattice_transfer.h>
 #include <Grid/lattice/Lattice_basis.h>
+#include <Grid/lattice/Lattice_crc.h>
diff --git a/Grid/lattice/Lattice_crc.h b/Grid/lattice/Lattice_crc.h
new file mode 100644
index 00000000..142e2349
--- /dev/null
+++ b/Grid/lattice/Lattice_crc.h
@@ -0,0 +1,55 @@
+/*************************************************************************************
+
+    Grid physics library, www.github.com/paboyle/Grid 
+
+    Source file: ./lib/lattice/Lattice_crc.h
+
+    Copyright (C) 2021
+
+Author: Peter Boyle <paboyle@ph.ed.ac.uk>
+
+    This program is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License along
+    with this program; if not, write to the Free Software Foundation, Inc.,
+    51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+    See the full license in the file "LICENSE" in the top level distribution directory
+*************************************************************************************/
+/*  END LEGAL */
+#pragma once
+
+NAMESPACE_BEGIN(Grid);
+
+template<class vobj> void DumpSliceNorm(std::string s,Lattice<vobj> &f,int mu=-1)
+{
+  auto ff = localNorm2(f);
+  if ( mu==-1 ) mu = f.Grid()->Nd()-1;
+  typedef typename vobj::tensor_reduced normtype;
+  typedef typename normtype::scalar_object scalar;
+  std::vector<scalar> sff;
+  sliceSum(ff,sff,mu);
+  for(int t=0;t<sff.size();t++){
+    std::cout << s<<" "<<t<<" "<<sff[t]<<std::endl;
+  }
+}
+
+template<class vobj> uint32_t crc(Lattice<vobj> & buf)
+{
+  autoView( buf_v , buf, CpuRead);
+  return ::crc32(0L,(unsigned char *)&buf_v[0],(size_t)sizeof(vobj)*buf.oSites());
+}
+
+#define CRC(U) std::cout << "FingerPrint "<<__FILE__ <<" "<< __LINE__ <<" "<< #U <<" "<<crc(U)<<std::endl;
+
+NAMESPACE_END(Grid);
+
+
diff --git a/tests/core/Test_fft_matt.cc b/tests/core/Test_fft_matt.cc
index d4455a7e..d92fa94e 100644
--- a/tests/core/Test_fft_matt.cc
+++ b/tests/core/Test_fft_matt.cc
@@ -1,5 +1,4 @@
     /*************************************************************************************
-
     grid` physics library, www.github.com/paboyle/Grid 
 
     Source file: ./tests/Test_cshift.cc
@@ -29,7 +28,14 @@ Author: Peter Boyle <paboyle@ph.ed.ac.uk>
 #include <Grid/Grid.h>
 
 using namespace Grid;
- ;
+
+Gamma::Algebra Gmu [] = {
+  Gamma::Algebra::GammaX,
+  Gamma::Algebra::GammaY,
+  Gamma::Algebra::GammaZ,
+  Gamma::Algebra::GammaT,
+  Gamma::Algebra::Gamma5
+};
 
 int main (int argc, char ** argv)
 {
@@ -49,22 +55,7 @@ int main (int argc, char ** argv)
   GridCartesian         GRID(latt_size,simd_layout,mpi_layout);
   GridRedBlackCartesian RBGRID(&GRID);
 
-  LatticeComplexD     one(&GRID);
-  LatticeComplexD      zz(&GRID);
-  LatticeComplexD       C(&GRID);
-  LatticeComplexD  Ctilde(&GRID);
-  LatticeComplexD  Cref  (&GRID);
-  LatticeComplexD  Csav  (&GRID);
   LatticeComplexD    coor(&GRID);
-
-  LatticeSpinMatrixD    S(&GRID);
-  LatticeSpinMatrixD    Stilde(&GRID);
-  
-  Coordinate p({1,3,2,3});
-
-  one = ComplexD(1.0,0.0);
-  zz  = ComplexD(0.0,0.0);
-
   ComplexD ci(0.0,1.0);
 
   std::vector<int> seeds({1,2,3,4});
@@ -73,7 +64,6 @@ int main (int argc, char ** argv)
   pRNG.SeedFixedIntegers(seeds);
 
   LatticeGaugeFieldD Umu(&GRID);
-
   SU<Nc>::ColdConfiguration(pRNG,Umu); // Unit gauge
 
   ////////////////////////////////////////////////////
@@ -81,17 +71,78 @@ int main (int argc, char ** argv)
   ////////////////////////////////////////////////////
   {
     LatticeFermionD    src(&GRID); gaussian(pRNG,src);
+    LatticeFermionD    src_p(&GRID);
     LatticeFermionD    tmp(&GRID);
     LatticeFermionD    ref(&GRID);
+    LatticeFermionD    result(&GRID);
     
-    RealD mass=0.01;
+    RealD mass=0.1;
     WilsonFermionD Dw(Umu,GRID,RBGRID,mass);
     
-    Dw.M(src,tmp);
+    Dw.M(src,ref);
+    std::cout << "Norm src "<<norm2(src)<<std::endl;
+    std::cout << "Norm Dw x src "<<norm2(ref)<<std::endl;
+    {
+      FFT theFFT(&GRID);
 
+      ////////////////
+      // operator in Fourier space
+      ////////////////
+      tmp =ref;
+      theFFT.FFT_all_dim(result,tmp,FFT::forward);
+      std::cout<<"FFT[ Dw x src ]  "<< norm2(result)<<std::endl;    
+
+      tmp = src;
+      theFFT.FFT_all_dim(src_p,tmp,FFT::forward);
+      std::cout<<"FFT[ src      ]  "<< norm2(src_p)<<std::endl;
+      
+      /////////////////////////////////////////////////////////////////
+      // work out the predicted FT from Fourier
+      /////////////////////////////////////////////////////////////////
+      auto FGrid = &GRID;
+      LatticeFermionD    Kinetic(FGrid); Kinetic = Zero();
+      LatticeComplexD    kmu(FGrid); 
+      LatticeInteger     scoor(FGrid); 
+      LatticeComplexD    sk (FGrid); sk = Zero();
+      LatticeComplexD    sk2(FGrid); sk2= Zero();
+      LatticeComplexD    W(FGrid); W= Zero();
+      LatticeComplexD    one(FGrid); one =ComplexD(1.0,0.0);
+      ComplexD ci(0.0,1.0);
+    
+      for(int mu=0;mu<Nd;mu++) {
+	
+	RealD TwoPiL =  M_PI * 2.0/ latt_size[mu];
+
+	LatticeCoordinate(kmu,mu);
+
+	kmu = TwoPiL * kmu;
+      
+	sk2 = sk2 + 2.0*sin(kmu*0.5)*sin(kmu*0.5);
+	sk  = sk  +     sin(kmu)    *sin(kmu); 
+      
+	// -1/2 Dw ->  1/2 gmu (eip - emip) = i sinp gmu
+	Kinetic = Kinetic + sin(kmu)*ci*(Gamma(Gmu[mu])*src_p);
+	
+      }
+    
+      W = mass + sk2; 
+      Kinetic = Kinetic + W * src_p;
+    
+      std::cout<<"Momentum space src         "<< norm2(src_p)<<std::endl;
+      std::cout<<"Momentum space Dw x src    "<< norm2(Kinetic)<<std::endl;
+      std::cout<<"FT[Coordinate space Dw]    "<< norm2(result)<<std::endl;
+    
+      result = result - Kinetic;
+      std::cout<<"diff "<< norm2(result)<<std::endl;
+      
+    }
+
+    std::cout << " =======================================" <<std::endl;
+    std::cout << " Checking FourierFreePropagator x Dw = 1" <<std::endl;
+    std::cout << " =======================================" <<std::endl;
     std::cout << "Dw src = " <<norm2(src)<<std::endl;
     std::cout << "Dw tmp = " <<norm2(tmp)<<std::endl;
-    
+    Dw.M(src,tmp);
     Dw.FreePropagator(tmp,ref,mass);
 
     std::cout << "Dw ref = " <<norm2(ref)<<std::endl;
@@ -122,7 +173,7 @@ int main (int argc, char ** argv)
     ferm()(0)(0) = ComplexD(1.0);
     pokeSite(ferm,src,point);
 
-    RealD mass=0.01;
+    RealD mass=0.1;
     WilsonFermionD Dw(Umu,GRID,RBGRID,mass);
 
     // Momentum space prop