Introduction10
Combined Arithmetic Operation. Any time a new number is entered after an operation, the HP-65 performs an automatic ENTER  on the result of that operation. This feature allows you to work serial calculations as well as chain and mixed chain calculations. Notice that we implicitly used this in the following:
Sample Case:
 
[(4×5) / (2+3)] – 6 = –2    
Press       See Displayed
4 ENTER       
  4.00
5 ×      
  20.00
2 ENTER       
  2.00
3 +      
  5.00
3 ÷      
  4.00
6      
2.00
   
Notice that the numbers are entered in the same order as they appear in the problem. Now consider the stack contents as we do the same example.
Stack Register
 
T                      
Z           20 20        
Y   4 4   20 2 2 20   4  
X 4 4 5 20 2 2 3 5 4 6 –2
 
 
Keys 4   5 × 2   3 + ÷ 6
Note: ENTER  is here abbreviated as  .