anchor.diff:  
   encode_pc(PointCode) when is_integer(PointCode) ->
   	case PointCode of
  -		undef ->
  +		undefined ->
   			{0, <<>>};
   		_ ->
   			{1, <<PointCode:16/little>>}
  
positive.code: 			<<SSN:8, Remain/binary>> = BinSSN;
  		_ ->
  			Remain = BinSSN,
  			SSN = undef
  	end,
  	{Remain, SSN}.
  
  
negative.code: 			<<PointCode:16/little, Remain/binary>> = BinPC;
  		_ ->
  			Remain = BinPC,
  			PointCode = undefined
  	end,
  	{Remain, PointCode}.
  
  