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# Calculator blog

Musings and comments about our common interest

## How I have configured my HP15c for financial duties (III)

The NPV and IRR are other favourites. There is another program in the Advanced Functions Handbook, that allows for up to 24 groups of cashflows (assuming you do not have any other program in memory!) and using 68 steps. However, as I said before, in my company we limit Capital Expenditure Proposal analysis to 10 years, so that I set to make a shorter program for 10 cashflows.

Register 0 is for the initial investment. Register ,1 contains the number of years to calculate (good to limit the loop and increase speed). Registers 1 to ,0 contain the flows of each year.

The system takes X as discount rate (in %). It can be then used to find the IRR through the Solve feature, entering a bracket of guesses in X and Y.

Now we come to a weighted average calculator. In many occasions I need to get the average margin of all the brands we sell.

But the weighting in HP12c works inverse as I would do. It calculates the average of Y weighted by X, instead of the average of x weighted by Y.

The calculators is mine and I do as I want with it ;-), so I will put it here, together with a cash discount calculation/comparison. We assign the weighted average to the same key, i.e. GSB 0:

One of the typical decisions in my job is to decide on cash discounts - both when buying and selling. I want to compare the cash discount % with a yearly rate - and then decide. I put the standard payment days in Y, and the discount % in X, and get the equivalent yearly interest that I am getting (if I'm buying) or I'm paying (if I'm selling)

Here it is:

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## How I have configured my HP15c for financial duties (II)

Here you have a small function missing in the 15c: the %T !!

I have placed it close to its siblings: in the GSB 7 key:

I loved its simplicity since I saw it in an HP41cv manual:

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## How I have configured my HP 15c for financial duties

As I have mentioned before, most of my duties involve financial calculations in an industrial environment.

The calculator I prefer among all, because of its simplicity (no menus) and its portability (fits in my jacket and occupies very limited space in a crowded desk, is the HP15.

Here is a dump of the program memory:

Let's start with an oldie, in the version that appears in the Advanced Functions handbook - no change needed. It uses the A to E keys in User mode, following the standard n -i- PV- PMT-FV. One key for entering the data and placing the program pointer in the right place; then R/S to execute:

I will continue in the next few blogs with the rest of the memory. For the sake of engineer futility, I have left space enough for a 3x3 + 3 equation system if some time was needed - and it has not been the case so far !!

 Time Value of Money 1 LBL A 2 STO 1 3 R/S 4 GSB .1 5 LST X 6 R/S 7 RCL*0 8 RCL 5 9 X<>Y 10 - 11 LST X 12 RCL+3 13 X=0? 14 GTO .0 15 / 16 CHS 17 TEST 4 18 GTO .0 19 LN 20 RCL 6 21 LN 22 / 23 STO 1 24 RTN 25 LBL B 26 STO 2 27 R/S 28 , 29 2 30 ENTER 31 EEX 32 CHS 33 3 34 CF 1 35 SOLVE .3 36 GOTO .4 37 GOTO .0 38 LBL .4 39 EEX 40 2 41 * 42 STO 2 43 RTN 44 LBL C 45 STO 3 46 R/S 47 GSB .1 48 GSB 2 49 CHS 50 STO 3 51 RTN 52 LBL D 53 STO 4 54 R/S 55 1 56 STO 4 57 GSB .1 58 RCL 3 59 GSB 2 60 X<>Y 61 / 62 CHS 63 STO 4 64 RTN 65 LBL E 66 STO 5 67 R/S 68 GSB .1 69 RCL+3 70 RCL+7 71 CHS 72 STO 5 73 RTN 74 LBL .1 75 SF 1 76 1 77 RCL 2 78 / 79 LBL .3 80 STO 8 81 1 82 STO 0 83 + 84 TEST 4 85 GOTO .0 86 STO 6 87 F?0 88 STO 0 89 RCL 1 90 CHS 91 Y^X 92 STO 7 93 1 94 X<>Y 95 - 96 X=0? 97 GOTO .0 98 RCL*0 99 RCL 4 100 RCL/8 101 * 102 F?1 103 RTN 104 RCL+3 105 LBL 2 106 RCL 5 107 RCL*7 108 + 109 RTN
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