diff --git a/ex4.2/CaloGrid.cc b/ex4.2/CaloGrid.cc
index bc4f79a..cd557f0 100644
--- a/ex4.2/CaloGrid.cc
+++ b/ex4.2/CaloGrid.cc
@@ -2,13 +2,13 @@
 #include <iostream>
 #include "CaloGrid.hh"
 
-CaloCell* CaloGrid::cell(int x, int y ) {
-	if ( x > nx or x < 0 ) {
+CaloCell* CaloGrid::cell( int x, int y ) {
+	if ( x >= nx or x < 0 ) {
 		std::cout << "CaloGrid::cell() Error: out of grid (x)" << std::endl ;
 		return nullptr;
 	}
 
-	if ( y > ny or y < 0 ) {
+	if ( y >= ny or y < 0 ) {
 		std::cout << "CaloGrid::cell() Error: out of grid (y)" << std::endl ;
 		return nullptr;
 	}
diff --git a/ex4.2/CaloGrid.hh b/ex4.2/CaloGrid.hh
index 28e1caa..decad8b 100644
--- a/ex4.2/CaloGrid.hh
+++ b/ex4.2/CaloGrid.hh
@@ -26,7 +26,7 @@ class CaloGrid
 
 		CaloCell* cell(int x, int y);
 		const CaloCell* cell(int x, int y) const {
-			return const_cast<CaloCell*> (cell(x, y));
+			return const_cast<CaloGrid*>(this)->cell(x, y);
 		}
 
 
@@ -44,7 +44,7 @@ class CaloGrid
 			// set Cell Ids
 			for ( int i = 0; i < nx ; i++ ) {
 				for ( int j = 0; j < ny ; j++ ) {
-					cells[i*ny +j].setId( i*ny+j );
+					cells[ i*ny+j ].setId( i*ny+j );
 				}
 			}
 		}
diff --git a/ex4.2/main.cpp b/ex4.2/main.cpp
index a4c0faf..56cdd3a 100644
--- a/ex4.2/main.cpp
+++ b/ex4.2/main.cpp
@@ -4,6 +4,10 @@
 #include "Point.hh"
 #include "Calorimeter.hh"
 
+void printCellId( const CaloCell* cell ) {
+	std::cout << cell->getId() << std::endl;
+}
+
 int main() {
 	CaloCell cell(0, 1) ;
 	Point p ;
@@ -13,11 +17,18 @@ int main() {
 
 	grid.cell(1, 1);
 
-	int nx = 2;
-	int ny = 2;
+	int nx = 3;
+	int ny = 4;
 
 	Calorimeter calo(nx, ny) ;
 
-	std::cout << calo.grid().cell(0,0)->getId() << std::endl;
-	std::cout << calo.grid().cell(nx-1,ny-1)->getId() << std::endl;
+	std::cout << "CellId at Start: " << calo.grid().cell(0,0)->getId() << std::endl;
+	std::cout << "CellId at End: "   << calo.grid().cell(nx-1,ny-1)->getId() << std::endl;
+
+	std::cout << "CellId at Center: " ;
+	printCellId(calo.grid().cell(nx/2,ny/2));
+
+
+	const CaloGrid grid2(5,5);
+	grid2.cell(3,3);
 }