HP-65 Annuity Program with Unknown Interest Rate

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I've had a lot of visitors but few comments! Let me hear from you! Email me at: Genewright143@hotmail.com

The program listed below will solve for the interest rate in the TVM equation provided that three of N, PMT, PV, or FV are known. It originally appeard in the 1975 PPC Journal, V2N6 Pages 14 and 15 by Neil Murphy (thanks to Neil wherever he is today!). This along with it’s companion program to solve for the interest rate were phenomenal programs at the time. The HP-65 Finance 1 card library had been introduced with 38 cards of programs in it. 12 of those cards were to solve the TVM problems handled by these two programs. If only factory written software.... ;-) Link:HP-65 Annuity Program with a Known Interest Rate

Instructions:

1) Initialize. Ordinary Annuity (payments at end of period), F-1, SF-1. (Clear Flag 1)
Annuity Due (payments at beginning of period), F, SF-1. (Set Flag 1)

2) Clear Registers. F, REG

3) Inputs (in any order)
N (number of periods). Press A. Display shows 0.00
PMT** (payment). Press C. Display shows 0.00
PV (present value). Press D. Display shows 0.00
FV** (future value). Press E. Display shows 0.00

** When calculating a sinking fund or periodic savings, either payment or future value (but not both) must be entered as a negative value.

4) Outputs or solve for...
I (interest rate PER PERIOD). Press B. Display shows the periodic interest rate.

Note: This program does NOT automatically store the calculated value into the corresponding storage register!

Program Listing. Keying in HP-65 programs can be a real pain for several reasons, but especially because it doesn’t show any line numbers for each instruction. Giving HP the appropriate break (since the HP-65 WAS the first handheld programmable), it’s still hard to do. It’s especially troublesome if you make a mistake since there is no BST function to see what you just typed in. If your HP-65 keyboard is sticky, you might get several instructions inserted into the program or it might not get inserted at all. Be sure to review the listing keycode by keycode after you have it typed in. ALSO, for those of you trying to make sense of this listing, remember: the HP- 65 skipped TWO steps after each conditional test, rather than the 1 step on all other HP’s!

Explanations. X NE Y? is x not equal to y. TF-1 is test flag 1 (the same as FS? 01 on later HP’s). F is the yellow function key so labeled. g RDN is the blue shift key followed by the roll down key. g RUP is the blue shift key followed by the roll up key. For any other questions, email me.

Examples: For examples, check out the other two Time Value of Money programs I have online and input the proper values from the listed examples section.

```Line   Keycode  Instruction
00	34 01	RCL 1
01	34 03	RCL 3
02	71	*
03	34 04	RCL 4
04	51	-
05	34 05	RCL 5
06	61	+
07	34 04	RCL 4
08	34 05	RCL 5
09	61	+
10	34 01	RCL 1
11	71	*
12	81	/
13	02	2
14	71	*
15	33 02	STO 2
16	23	LBL
17	01	1
18	34 02	RCL 2
19	01	1
20	61	+
21	33 06	STO 6
22	34 01	RCL 1
23	35	g
24	05	Y^X
25	33 07	STO 7
26	34 04	RCL 4
27	71	*
28	34 05	RCL 5
29	51	-
30	34 03	RCL 3
31	81	/
32	34 02	RCL 2
33	71	*
34	34 06	RCL 6
35	34 02	RCL 2
36	31	F
37	61	TF-1
38	34 07	RCL 7
39	71	*
40	51	-
41	34 07	RCL 7
42	51	-
43	61	+
44	35 00	g LSTX
45	34 02	RCL 2
46	81	/
47	32	F-1
48	61	TF-1
49	34 06	RCL 6
50	81	/
51	61	+
52	34 01	RCL 1
53	34 02	RCL 2
54	71	*
55	34 05	RCL 5
56	71	*
57	34 03	RCL 3
58	81	/
59	34 06	RCL 6
60	81	/
61	51	-
62	81	/
63	34	STO
64	61	+
65	02	2
66	35	g
67	06	ABS
68	43	EEX
69	42	CHS
70	06	6
71	35 22	g X<=y? 72 22 GTO 73 01 1 74 34 02 RCL 2 75 43 EEX 76 02 2 77 71 * 78 24 RTN 79 23 LBL 80 11 A 81 33 01 STO 1 82 24 RTN 83 23 LBL 84 13 C 85 33 03 STO 3 86 24 RTN 87 23 LBL 88 14 D 89 33 04 STO 4 90 24 RTN 91 23 LBL 92 15 E 93 33 05 STO 5 94 24 RTN ```

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