Section 4: Programming 269
  Press   Comment  
  4000   STO 1   Initial downpayment  
      STO 2   ($4000).  
  1.005   STO 3   Monthly inflation factor  
  2000   STO 4   Initial savings  
      STO 5   ($2000).  
  185   STO 6   Monthly savings  
  1.01   STO 7   Monthly interest factor  
Note that the initial downpayment is both R1 and R2. This is because in our program r1 will remain the same as the initial value but R2 will contain the downpayment in successive months. We can at will reset R2 to the initial value saved in R1 and start over again. The same reasoning holds for R4 and R5 containing the initial savings.
One final word before we actually start our program. Normal procedure is to write the entire program sequence, enter it, and then test it. For the sake of greater understanding, we will write one label at a time and obtain the answers for that segment of the problem as we go along.

Programming Label A : Monthly Total Downpayment

1. Switch to W/PRGM.
2. Press fPRGM to clear memory.
3. Key in the sequence of steps below.
LBL 23  
A 11  
RCL 2 34 02 Dnpmt
RCL 3 34 03 Inflation factor
× 71  
STO 2 33 02 New dnpmt
RTN 24  
  Dnpmt × 1.005 = New Dnpmt