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The program listed below provides several useful business functions for the HP-65 calculator. It was originally written by C.W. Burt and J.J. Reymond (My thanks to them wherever they are today).

It provides Percent, Percent of Sum, Mean, Standard Deviation, and Future Value of a Compound Amount. All in 99 program steps! Several examples are given below.

To compute the Mean and Standard Dev. of 100, 80, 90, and 95:
1. Press E to initialize.
2. Key 100 R/S, (See 1 displayed), Key 80 R/S, (See 2 displayed, etc.), Key 90 R/S, Key 95 R/S.
3. To correct an entry, enter the value and press RTN R/S.
4. To compute the Mean, Press C. See 91.25.
5. To compute the Standard Deviation, Press RTN C. See 7.40

To find X% of Y: What is 10% of 50, 1. Press E to initialize.
2. Key 50, ENTER, 10, D. See 5 displayed.

To find the percent of a total (or sum): What percent of 250 is 80? 1. Press E to initialize.
2. Key 250, ENTER, 80, RTN, R/S. See 32 displayed.

To find the future value of a compounded amount: What is the amount in a savings account if you deposit \$1500 today at 8% compounded quarterly for 10 years?

1. Press E to initialize.
2. Enter interest rate of 2% (8 divided by 4): 2, RTN, A
3. Enter present value of \$1500: 1500, RTN, B
4. Enter number of periods and compute future value: 10 years times 4 periods per year: 40, A. See 3312.06 displayed.

Program Listing. This program was really a remarkable achievement, given the space limitations of the HP-65. Here's the program. f-1 is the HP-65 "Inverse" prefix key. f is the yellow prefix key. I've provided the key codes that show up in program memory, especially since the HP-65 doesn't show the program step number in the display. Lines 71 and 72 will show up as keycodes 35 and 05. Notice how RCL 1 is a merged step, but STO - 3 takes three steps!
```Line  Code   Function
01    32        f-1
02    09        SQRT
03    33        STO
04    51        -
05    03        3
06    35 00  g LastX
07    33        STO
08    51        -
09    02        2
10    34 01  RCL 1
11    01        1
12    51        -
13    33 01  STO 1
14    15        E
15    23        LBL
16    11        A
17    01        1
18    00        0
19    00        0
20    81        /
21    01        1
22    61        +
23    33 01  STO 1
24    15        E
25    23        LBL
26    12        B
27    33 02  STO 2
28    15        E
29    23        LBL
30    13        C
31    32        f-1
32    09        SQRT
33    34 01  RCL 1
34    71        x
35    51        -
36    34 01  RCL 1
37    81        /
38    31        f
39    09        SQRT
40    15        E
41    23        LBL
42    14        D
43    35 07  g X<>Y
44    81        /
45    35 00  g LastX
46    35 07  g X<>Y
47    43        EEX
48    02        2
49    71        x
50    23        LBL
51    15        E
52    84        R/S
53    32        f-1
54    09        SQRT
55    33        STO
56    61        +
57    03        3
58    35 00  g LastX
59    33        STO
60    61        +
61    02        2
62    34 01  RCL 1
63    01        1
64    61        +
65    33 01  STO 1
66    15        E
67    23        LBL
68    11        A
69    34 01  RCL 1
70    35 07  g X<>Y
71    35        g
72    05        Y^X
73    34 02  RCL 2
74    71        x
75    34 02  RCL 2
76    35 07  g X<>Y
77    15        E
78    23        LBL
79    12        B
80    35 07  g X<>Y
81    15        E
82    23        LBL
83    13        C
84    34 03  RCL 3
85    34 02  RCL 2
86    34 01  RCL 1
87    81        /
88    15        E
89    23        LBL
90    14        D
91    43        EEX
92    02        2
93    42        CHS
94    71        x
95    35 07  g X<>Y
96    71        x
97    35 00  g LastX
98    35 07  g X<>Y
99    15        E```