Fun with the HP 30b
Introduction
The following programs are for the HP 30b Business Professional. Did you know that the 30b has a programming mode? The program mode has room for 10 programs with a total of 290 steps, where each key press is counted. Thankfully, shifts and hold-shifts are merged steps.
I couldn’t get the MSG or R/S commands to work properly. Therefore I use an approach that I often use for the Voyager calculators (HP 11C, 12C, 15C): store everything first and then run the program.
Disp5 is like the PSE (pause) command, it stops the execution for a second. Disp can be set to 1-9. Disp1 lasts for 1/5 second.
All programs are done in the Algebraic instead of the RPN I usually do on HP calculators.
All the results in the examples, except the last one, are rounded to four decimal places.
Program 0: f(x,y) = (x * y) / (x + y)
f(x, y) = (x * y) / (x + y)
Store x in memory 1 and y in memory 2.
Prog 0 =
RCL 1
×
RCL 2
÷
( ↓
RCL 1
+
RCL 2
) Swap
=
Stop
Examples:
x = 1.5, y = 16; Result: 1.3714
x = 3.6, y = 32; Result: 3.2360
x = 8.7, y = 10; Result: 4.6524
Program 1: PITI – Principal, Interest, Taxes, and Insurance
This program calculates the monthly payment of PI (principal and interest) and PITI (principal, interest, taxes, and insurance). The program assumes that payments per year setting (P/YR) is set to 12.
Store to Memory:
M1: Annual insurance rate.
M2: Annual property tax rate.
N: number of payments
I/YR: interest rate of the loan
PV: amount of the loan
It assumed that there is no balloon payment (FV = 0), although this program can be modified to include balloon payments by removing the first two steps (0 FV).
Prog 1 =
0
FV
PMT
Disp5
Disp5
-
( R↓
RCL 1
+
RCL 2
) Swap
/
1
2
0
0
*
RCL PV
=
Stop
Examples:
N = 360
I/YR = 8.9%
PV = 289000
Insurance Rate = 1% (1 STO 1)
Property Tax Rate = 1.3% (1.3 STO 2)
Result:
PMT: -2304.60
PITI: -2858.51
N = 360
I/YR = 8.9%
PV = 289000
Insurance Rate = 1% (1 STO 1)
Property Tax Rate = 1.3% (1.3 STO 2)
Result:
PMT: -2304.60
PITI: -2858.51
Program 2: Quadratic Equation – Po-Shen Lo Method
This program solves the monic quadratic polynomial:
x^2 + B * x + C = 0
where the solutions:
U^2 = B^2 / 4 – C
x1, x2 = - B / 2 ± √(U^2)
Store to Memory:
M1: B
M2: C
Prog 2 =
RCL 1
X^2
/
4
-
RCL 2
=
√
STO 0
-
RCL 1
/
2
=
STO 3
Disp5
Disp5
-
2
*
RCL 0
=
STO 4
Stop
M3: root 1 ( -B / 2 + √(U^2) )
M4: root 1 ( -B / 2 + √(U^2) )
This program finds real roots only. If there are no real roots, then the program displays an error.
Examples:
x^2 – 2 * x – 24 = 0
B = -2 STO 1
C = -24 STO 2
Roots: 6, -4
x^2 – 10 * x + 21 = 0
B = -10 STO 1
C = 21 STO 2
Roots: 3, 7
Program 3: Lease with Advanced Payments (HP 12C – see source)
This program calculates the regular monthly payment of a lease when the borrower pays a set number of payments in advance. Payments per year (P/YR) is assumed to be set at 12 while the calculator is set to End of Period payments.
Store in Memory:
number of payments [ N ]
annual lease rate [ I/YR ]
residual value [ FV ]
number of payments to be made in advance [ STO ] 0
loan amount [ STO ] 1 (not PV)
Prog 3 =
0
PMT
0
PV
PV
+
RCL 1
=
STO 2
0
FV
RCL N
-
RCL 0
=
N
1
+/-
PMT
( R↓
PV
+
RCL 0
) Swap
1/X
*
RCL 2
=
Stop
Examples:
Total Payments: 48 [ N ]
Rate: 13 [ I/YR ]
Residual Value: 7,000 [ FV ]
Payments in Advance: 1 [ STO ] 0
Loan Amount: 25,000 [ STO ] 1
Result: -536.06
Total Payments: 60 [ N ]
Rate: 8.8 [ I/YR ]
Residual Value: 12,000 [ FV ]
Payments in Advance: 3 [ STO ] 0
Loan Amount: 118,000 [ STO ] 1
Result: -2,229.71
For those of you in the United States, Happy Thanksgiving!
Source
Hewlett Packard. HP 12C Financial Calculator: User’s Guide. Edition 5. 2008. San Diego, CA. pp. 124-126
Eddie
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