The program will run as written on an HP-19C/29C, and with slight modification on an HP-34C, HP-11C, HP-15C. HP-67 users can either use the program provided in the standard pac or modify the one presented here for the HP-19C. HP-41C users should be using the PPC ROM FI program anyway. ;-)
This program is not very sophisticated when it comes to solving for the interest rate and can take up to a minute or so to find it. For all but bizarre financial problems, however, it should be OK. Be patient. If you have the HP-34C applications book, you really should use the program in it for TVM: it uses the Solve function for the interest rate.
1) Key in the program.
2) Initialize by 0, GSB 0 for an ordinary annuity; or a 1, GSB 0 for an annuity due.
3) Input known values as follows, using a zero for unknowns, and negative numbers for cash outflows and positive numbers for cash inflows:
N STO 1 I(%) STO 2 PMT STO 3 PV STO 4 FV STO 54) Calculate the unknown value:
N GSB 1 I(%) GSB 2 PMT GSB 3 PV GSB 4 FV GSB 5The result appears in the display and in the appropriate storage register.
5) For a new problem, go to step 2. For new values, go to step 3.
Line Keycode 01 LBL 0 15 13 00 02 STO.0 23 .0 03 RTN 15 12 04 LBL 1 15 13 01 05 GSB 6 12 06 06 RCL 9 24 09 07 RCL 5 24 05 08 - 41 09 RCL 9 24 09 10 RCL 4 24 04 11 + 51 12 DIV 71 13 LN 14 42 14 RCL 6 24 06 15 LN 14 42 16 DIV 71 17 STO 01 23 01 18 RTN 15 12 19 LBL 2 15 13 02 20 0 00 21 ENTER 31 22 1 01 23 ENTER 31 24 STO 2 23 02 25 % 15 21 26 X<>Y 21 27 LBL 7 15 13 07 28 DIV 71 29 STO+2 23 51 02 30 STO.3 23 .3 31 X<>Y 21 32 STO.1 23 .1 33 GSB 6 12 06 34 RCL 4 24 04 35 - 41 36 STOx.3 23 61 .3 37 STO-.1 23 41 .1 38 RCL.3 24 .3 39 RCL.1 24 .1 40 X NE 0 15 61 41 GTO 7 13 07 42 RCL 2 24 02 43 RTN 15 12 44 LBL 3 15 13 03 45 GSB 6 12 06 46 X<>Y 21 47 RCL 4 24 04 48 - 41 49 RCL 8 24 08 50 DIV 71 51 RCL.2 24 .2 52 X 61 53 STO 3 23 03 54 RTN 15 12 55 LBL 4 15 13 04 56 GSB 6 12 06 57 STO 4 23 04 58 RTN 15 12 59 LBL 6 15 13 06 60 RCL .0 24 .0 61 STO 0 23 00 62 1 01 63 STO 8 23 08 64 RCL 2 24 02 65 % 15 21 66 STOx0 23 61 00 67 STO.2 23 .2 68 ISZ 15 24 69 + 51 70 STO 6 23 06 71 RCL 1 24 01 72 CHS 32 73 Y^X 14 64 74 CHS 32 75 STO 7 23 07 76 STO+8 23 51 08 77 RCL 5 24 05 78 X 61 79 RCL 8 24 08 80 RCL 3 24 03 81 RCL 0 24 0 82 STOx8 23 61 08 83 X 61 84 RCL.2 24 .2 85 DIV 71 86 STO 9 23 09 87 X 61 88 - 41 89 RTN 15 12 90 LBL 5 15 13 05 91 GSB 6 12 06 92 LASTX 14 73 93 RCL 4 24 04 94 + 51 95 RCL 7 24 07 96 DIV 71 97 STO 5 23 05 98 RTN 15 12That's it. A few of the above lines need some explanation.
Lines 12, 16, 28, 50, 85, and 96 are the Divide function. Line 40 is the conditional test "X not equal to Zero". Lines where you see STO.3 are actually storing into memory 13. HP used this trick to save instructions in some calculators.To translate this program to the HP-34C, HP-11C, or HP-15C, a couple of changes are needed:
(a) Lines 36 and 37 cannot be entered on the 34C or the HP-11C. This was something I didn't know until I was keying this into the 34C. Storage register arithmetic is only available on the 34C on the primary registers 0-9. What to do? Replace lines 36-39 of the above program with: ENTER, ENTER, RCL.3, X<>Y, X, RCL.1, LASTX, -, where the X right before the RCL.1 is a Multiply.
(b) Line 68 (ISZ) should be replaced with 1, STO+ 00, RDN, where RDN is Roll Down. This applies to the 34C, 11C, 15C.
(c) for the HP-15C, Change step 40 to be TEST 0 (Which is the HP-15C version of X NE 0), and make the change (b) just given for the 34C.
(1) Suppose you're going to buy a $200,000 house with a 30 year mortgage, at 8% compounded monthly. What is your monthly house payment?
Initialize: 0, GSB 0.
Key: 360, STO 1, 8 ENTER 12 DIV, STO 2, 200000, STO 4, 0, STO 5, GSB 3.
Answer is : -$1467.53.
Check for proper program entry by doing the following:
GSB 1 should show 360.00 GSB 2 should show 0.67 (which when multiplied by 12 is 8%) GSB 4 should show 200000.00 GSB 5 should show 0.00
(2) Given the problem above and that you have solved it, suppose you only made payments of $1400 a month? What is the balance left to be paid at the end of the 30 year period?
If you haven't changed any values in memories 1-5 since the last example, key 1400 CHS STO 3. GSB 5.
Answer is -$100,642.70. Wow, better find a way to come up with that extra $67.53 a month.
(3) What is the yield on a 20 year semiannual bond with a coupon rate of 8%, that is currently selling for $900? (Assuming the maturity value is $1000)
Since the bond is semiannual, Initialize: 0, GSB 0. Key 40 STO 1, -40 STO 3, 900 STO 4, -1000 STO 5. GSB 2.
Answer is : 4.5471. This is the semiannual yield, so multiply by 2 and the true yield is 9.09%.