Example 3.7
 Interplanar spacing is  2.027 angstrom 

 For a^2/d^2 = 2 	 Reflection plane is {110}
 For a^2/d^2 = 4 	 Reflection plane is {200}
 For a^2/d^2 = 6 	 Reflection plane is {211}
 For a^2/d^2 = 8 	 Reflection plane is {220}