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Hidden Treasures: The other calculators, Pt 2

Thu Jul 20, 2006 - 3:27 PM EDT - By Jay Gross


Here's a real money maker. Or not. We often need the functions of the Treos' Finance calculator, even if we don't know it. This one makes everybody a tycoon. Use it to calculate the future value of an investment, or figure out the required present value of something, given its value at some future time.

Besides the basic arithmetic functions on the center buttons, the Finance calculator provides an Edit screen (see the Edit button, left side, second row?), in which you can solve the equations known as Time Value of Money for present and future value without knowing the equation, and without laboriously implementing it in a spreadsheet's cell formulae.

The Treo's equation deals only with evenly spaced, equal cash flows (Payments), which can be either intake or outgo. Tap the Edit button and let's take a look. The monikers are all jargon to the finance set, but here they are in English:
  • Begin/End (toggle) – This tells the program whether payments are made at the beginning of a period (in advance, like rent), or at the end (like interest accrual)
  • Payments per year
  • Present Value
  • Future Value
  • Payment Amount
  • Annual Percentage Rate – this is also known as I/Y
  • N (Number of periods, or "term" of the loan, mortgage, or investment)
Put in all but one of these, and the Treo will figure out the missing item when you tap the "Solve" button. Doesn't matter which one you omit, either. To erase the content of a field, highlight with the stylus and press the Backspace button on the keypad. The Edit screen has no pulldown menus.

The Treo's Finance calculator does not provide variables for compounding, or for Beginning/Ending lump sum payments like you'd have on a lease. Have to figure those on your own. Plus or minus indicates the direction of cash flow. "Flow" - isn't that a nice term to apply to cash? Anyway, inflow is positive, and outflow is negative.

If this is a mortgage or an installment loan, you can get an amortization table easy as blueberry pie. Just solve the equation, tap the Done button, and then tap "Amrt".

As with all the calculators, you can copy the results to the clipboard and paste into another application – like an SMS message, an email, or a memo. However, this does not work in the Amortization windows. Touch the stylus to the screen to highlight a row of information – Principal, Interest, and Balance.

The buttons across the top of the calculator's screen do the same thing as entering the information into the Edit screen. The other buttons do what they look like they might do, but not what they would on a non-financial calculator.

  • % -- percent
  • Delta% -- percent change
  • %? – compute percentage
  • Delta%? – compute percent change

    Percent applies a percentage to the number you specify. So, if you want to know what is 35% of some number, tap the number, then %, then the = button. Tap 56.95, %, 25, = 14.2375.

    Percent change computes the total that results after applying a percentage, plus or minus, to it. For example, that antique Tux penguin in your geek boutique at an 85% markup. Tap 5.50 (your cost), Delta%, 85, and the big = button. The penguin's price tag is $10.18.

    The %? button computes "What percentage of this is that?" The first number you enter is the comparator, and second is the comparatee. So, first number 100, second number 50. It's like asking "What percentage of 50 is 100?" Tap 100, %?, 50, and the answer is 200.

    Delta%? is similar. It figures out by what percentage you'd have to multiply the second number to get the first. Enter 100, tap Delta%?, tap 85 and =. You'd reap a 17.6470588% markup on an $85 item to charge $100 for it.

    Example: That new car you want to buy me has a $50,000 sticker price. You can finance it at Greedmongers Bank and Trust for 5% annual percentage rate on a 24-month term, and the payments will be… you figure it out. And please send over the ignition key soon.

    Example: Monthly payment on a $75,000 thirteenth mortgage, 30 years at 5.5% annual percentage rate. Set Begin/End to END.

    Set Payments / year to 12
    Set PV to 75000
    Set FV to 0
    Erase any entry in Pmt and leave it blank (not 0, blank!)
    Set APR to 5.50
    Set N to 360 (=30 years times 12 payments per year)

    Tap Solve and the payment amount appears in the Pmt line: 425.84175101025.

    Using the Amrt function, you find out that the last payment tidies up $423.90 of principal and $1.94 interest, leaving a balance of zip. The payment has a negative sign because it's cash out. To have the calculator allow for beginning and ending payments, subtract them (add, if it's cash incoming) from the present and future values. So, $75000 minus your $12,500 down payment leaves a mortgage of $62,500.

    Another useful example: Money in savings accounts (wise). If you open an account for, say, $5,000, how much will you have after 20 years at 5% interest?

    Set Begin/End to END
    Enter 12 for payments per year (monthly)
    Enter 5000 for PV
    Clear the FV line entirely
    Enter 0 of Pmt (we don't need that variable)
    Enter 0.50 for APR
    Enter 240 for N (5 years, in months)

    Tap Solve and you get a FV of 5,525.7395015745

    Your mileage will vary according to the number of times during a year the interest is compounded. For example, the TI model BA-plus calculator assumed a quarterly compounding and came up with $5,524.48 instead.


    The Treo 650 and 700P include powerful math, trigonometry, and financial calculators, and that's just the beginning. Curious that the powerful features aren't documented in Treo manuals, but the information in this and the next part of this continuing saga should get you going.

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