Electronically Checking Overflow

Look at the answer: since the carry into the high order column is the same as the carry out of the high order column, the result is correct. We don't need to figure out what decimal numbers the patterns represent.

11111 1 1
 1011 1101  
 1110 0101  
 1010 0010  

The electronics of a computer determine if a calculation is correct by using a simple circuit that tests the equality of the carry-in bit and the carry-out bit of the high order column. However, when you do a calculation with paper and pencil you can check your work by translating the operands and results into decimal:

11111 1 1
 1011 1101 
 1110 0101 
 1010 0010  

 
-67 
-27   
-94 

Of course, the computer has no independent means of "checking its result." All it can do is look at the carry bits into and out of the high order column.