Retro Review: Texas Instruments Financial Investment FIA-10

Retro Review:   Texas Instruments Financial Investment FIA-10

Possibly a predecessor to the well known BA-II Plus, the FIA-10 introduced financial worksheets for various financial applications.  

Quick Facts

Model:  FIA-10

Company:  Texas Instruments

Years:  1988 - 1990

Type:  Finance

Batteries: 1 x CR-2032

Operating Modes:  Chain

Number of Registers: 10

Display:  large display, 5 lines for variables, 1 line for calculations 

A Collector's Calculator

The FIA-10 is a collector's calculator! The FIA-10 is a financial calculator has a large screen with five soft keys located to the right side of the screen.  There is a sixth button, Compute, is used to solve for variables.  

The FIA-10 has ten worksheets.  Each worksheet has up to four columns, in which each column can have a separate list of data.

1.  Time Value of Money/Amortization:  4 columns

2.  Cash Flow including net present value, net future value, internal rate of return:  2 columns

3.  Bond Calculations:  yields and prices:  4 columns

4.  Depreciation:  including straight line, sum of the year's digits, declining balance:  1 column

5.  Statistics with Linear Regression: 1 column

6.  Interest Conversions between APR and EFF/NOM:  1 column

7.  Percent Change: 1 column

8.  Profit:   cost vs. selling price vs. margin:  1 column

9.  Date Calculation:  for dates from October 15, 1982 to February 28, 4000:  1 column

10.  Memory:  up to ten memory registers R0- R9 can be seen in this worksheet:  1 column

Storage arithmetic is allowed  (STO+, STO-, STO×, STO÷, STO^).  Any variable can be recalled by using the [ RCL ] key.   

In short, this rare calculator is worth collecting.  If you are familiar with the BA II Plus, the FIA-10 will be easy to work with.  

Eddie 

All original content copyright, © 2011-2022.  Edward Shore.   Unauthorized use and/or unauthorized distribution for commercial purposes without express and written permission from the author is strictly prohibited.  This blog entry may be distributed for noncommercial purposes, provided that full credit is given to the author. 

HP 12C: Cash Back vs Credit Card Interest

HP 12C: Cash Back vs Credit Card Interest

Introduction

If you have a credit card, chances are that you have a cash back program, where the company offers you cash back rate based on qualified purchases.  Is the benefit worth it?  

HP 12C Program:  Cash Back vs. Interest

Store the following data:

PV:  current credit card balance

PMT:  qualified purchases

i% using [ g ] (12÷):  monthly credit card rate

R0 using [ STO ] 0:  cash back rate

This program assumes all purchases made qualify for the cash back rate.

Step #;  Step Key;  Key

01; 45, 14; RCL PMT

02; 45, 0;  RCL 0

03; 25; %

04; 31; R/S

05; 45, 13; RCL PV

06; 45, 14; RCL PMT

07; 40;  +

08; 45, 12; RCL i

09; 25; %

10; 31; R/S

11; 40; +

12; 43,33,00; GTO 00   (use GTO 000 on HP 12C Platinum)

Outputs:

1.  Cash back 

2.  Interest charged on the balance and purchases

3.  New balance

Examples

Example 1:

Credit card balance:  $1,000.00   

Qualified purchases:  $230.00

Credit card annual rate:  15%

Cash back rate:  5%

1000 [ PV ]

230 [ PMT ]

15 [ g ] (12÷)

5 [ STO ] 0

[ R/S ]:

11.50  [ R/S ]

15.38  [ R/S ]

1241.50

Cash back:  $11.50

Interest:  $15.38

New balance:  $1,241.50

Example 2:

Credit card balance:  $585.65   

Qualified purchases:  $176.19

Credit card annual rate:  16.79%

Cash back rate:  5%

585.65 [ PV ]

176.19 [ PMT ]

16.79 [ g ] (12÷)

5 [ STO ] 0

[ R/S ]:

8.81 [ R/S ]

10.66  [ R/S ]

772.50

Cash back:  $8.81

Interest:  $10.66

New balance:  $772.50

Investigation:  Cash Back Benefit vs. Credit Card Interest

I then wondered, is there a point where the cash back gives a better benefit than the interest charged.

Consider the equation:

cash back benefits = monthly interest charge

purchases * cash_back% = (balance + purchases) * monthly_interest%

purchases * (cash_back% - monthly_interest%) = balance * monthly_interest%

purchases * (cash_back% ÷ monthly_interest% - 1) = balance 

cash_back% ÷ monthly_interest% - 1 = balance ÷ purchases

Let the test ratio be defined as:

test ratio = cash_back% ÷ monthly_interest% - 1 

Using the data from Example 2:

test ratio = 5 ÷ (16.79 ÷ 12) - 1 ≈ 5 ÷ 1.40 - 1 ≈ 3.57 - 1 = 2.57

For the cash back and interest to be equal, the purchases must equal balance÷2.57 or $227.88.  Running the program, the cash back and interest charged is around $11.38.  

This means we will have to make a lot of qualified purchases.  Say if we spent $400.00 in purchases, the cash back is $20.00, with interest $13.79, and the balance $999.44.  

To try to do this on a continuous basis poses several problems:  we still have to pay the balance otherwise we have to buy more each month to get the greater benefit.  Also, the lower the starting balance, the lower the minimum purchase requirement.

With a credit card rate of 16.79% (monthly about 1.40%) and cash back 5%, the test ratio is (5 ÷ 1.4 - 1) is 2.57.  

A beginning balance of $200.00 will require $77.82 of qualified purchases (200 ÷ 2.57), while a beginning balance of $500.00 will require $194.55 in purchases.

Take care and have a great day,

Eddie

All original content copyright, © 2011-2022.  Edward Shore.   Unauthorized use and/or unauthorized distribution for commercial purposes without express and written permission from the author is strictly prohibited.  This blog entry may be distributed for noncommercial purposes, provided that full credit is given to the author. 

Retro Review: Texas Instruments BA-Solar

Retro Review: Texas Instruments BA-Solar

Finance + Solar + 1980s

Quick Facts

Model:  BA-Solar

Company:  Texas Instruments

Years:  1986 - 1990s; a refresh , BA-35 SOLAR was produced 1996-2000s

Type:  Finance

Batteries: Solar 

Operating Modes:  Chain

Number of Registers: 1, |MEM|

Display:  1 line, 10 digits

Features

The [ MODE ] key is used to toggle between three modes:

FIN Mode:  Time Value of Money  (FIN indicator)

N:  number of payments

%i:  periodic interest rate

PV:  present value

PMT:  payment

FV:  future value

The current cash flow convention is not used, instead the following equation is (I think) used in solving time value of money calculations: 

PV = FV *  SPPV + PMT * USPV

SPPV = single present value factor

USPV = present value annuity factor

We also have amortization functions:

BAL:  balance after any payment

I/P:  interest and principal at any payment

payment_1 P1/P2 payment_2 I/P:  cumulative interest and principal

There are ×12 and ÷12 aids, but we still have to press [ N ] and [ %i ] to register the values, they are not automatic.  

STAT Mode:  Statistics  (STAT indicator)

The BA-SOLAR (and the later BA-35 SOLAR) has both single variable statistics and linear regression.

In linear regression, use the [x<>y] key to change between x and y.   The key will also be used to switch between results.  

Prediction values can be calculated with x' and y'.

The equation used for linear regression is y = a*x + b,  a = slope, b = intercept.

Profit Mode (no indicator)

The profit mode makes the following solver available:

CST:  cost

SEL:  sell

MAR:  margin

MU:  markup

Functions Available in All Modes

Percent Calculations (%):

Add %:  x [ + ] y [ % ] [ = ]

Subtract %:  x [ - ] y [ % ] [ = ]

Multiply %:  x [ × ] y [ % ] [ = ]

Percent Ratio:  part [ ÷ ] whole [ % ] [ = ]

Percent Change:  new [ 2nd ] ( ⊿% ) old [ = ]

rate >EFF payments/year:  convert to effective rate

rate >APR payments/year:  convert to APR/nominal rate

Mathematics:

Natural logarithm and antilogarithm:  ln x, ^x

Square and square root

Power

Reciprocal

Final Thoughts

This is a great basic financial calculator.  I have both the BA-SOLAR and BA-35 SOLAR.   To be honest, I like the keyboard of the original BA-SOLAR better, the keys feel a bit more solid and responsive.  Even though they are no longer in production, the BA-SOLAR is still reasonably available on sites such as eBay and other online stores.  

Source:

Woerner, Joerg.  "Texas Instruments BA-SOLAR"  Last Updated December 5, 2001.   http://www.datamath.org/Sci/Modern/BA-SOLAR.htm   Retrieved May 19, 2022.

Eddie

All original content copyright, © 2011-2022.  Edward Shore.   Unauthorized use and/or unauthorized distribution for commercial purposes without express and written permission from the author is strictly prohibited.  This blog entry may be distributed for noncommercial purposes, provided that full credit is given to the author. 

Python: Financial Functions (2nd Edition)

Python:  Financial Functions (2nd Edition)

This is an update to the python file, which I first released on May 17, 2020:

https://edspi31415.blogspot.com/2020/05/numworkscasio-micropythonpython.html

I am able to transfer and test the python file to a Numworks calculator through the online editor, and TI-84 Plus CE Python through the TI Connect CE.  Because only the math module is used, the python file can be run in most, if not all calculators with Python, as well as Python 3.  

What is included?

*  time value of money calculations

*  net present value and internal rate of return

*  net present value (xnpv) and internal rate of return (xirr) when periods between flows are not consistent, a 365 day-year is assumed

*  simple interest:  calculating interest, total, and solving for principal

*  profit calculations: cost-sell-markup

*  adding sales tax

*  percent change

*  present and future value uniform stream factors

*  compound interest calculations of a single stream:  solve for present value, future value, number of periods, and periodic interest

*  days between dates

*  specific applications:  monthly payment, PITI, qualifying loan amount, sinking fund, expressing a list of amounts as a percent of the sum, prorating an amount among a list of flows

Download the Python file and the instructions (pdf file) here:

https://drive.google.com/file/d/1l7Xg9dM-RHfekKkU7A1Wjay76-yVc56S/view?usp=sharing

Size: about 3,800 bytes.  

Eddie

All original content copyright, © 2011-2020.  Edward Shore.   Unauthorized use and/or unauthorized distribution for commercial purposes without express and written permission from the author is strictly prohibited.  This blog entry may be distributed for noncommercial purposes, provided that full credit is given to the author.