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HP 20b Business Consultant Frequently Asked Questions
Over the years, I have received many questions about financial calculators. I will compile a list of the most frequently asked questions here.
Q: My 20b is showing a comma instead of a decimal point. How do I fix this problem?
A: This is easily the most commonly asked question. I wish I knew how people got themselves into this situation, because it seems unlikely that it could happen by accident. Here is how to solve the problem: Press ( (this is the Mode key, which I will refer to as Mode from this point) and then scroll down the list 3 times until you see 1,23 (or 1.23) on the screen. Next, press INPUT to toggle the radix mark. Once set, press ON/CE to exit from Mode settings.
A little background on this. In the U.S. and many other countries, we use a decimal point as the radix point (or decimal separator) and a comma as the thousands separator. Many other countries do exactly the opposite. For a complete list, see the decimal separator article on Wikipedia. Interestingly, as far as I can tell this has nothing to do with the side of the road on which you drive. Obviously, the 20b was created with worldwide users in mind.
Q: How do I change the number of decimal places that are displayed?
A: Simply press Mode and you will see FIX = in the top line. This is the setting that you want to change, so enter a number of decimal places and then press INPUT. Press ON/CE to exit from Mode settings. For example, to display five decimal places, press Mode 5 INPUT ON/CE.
If you often change the number of decimal places displayed, there is a nice shortcut. Press and release the key and then press and hold the key while pressing a number key to indicate the number of decimal places to show. For example, to display 5 decimal places you would press and then 5.
If you ever need to see the full-precision answer, there is no need to change the number of decimal places. Instead, do you calculation and then press the 🠈 key, which is below RCL and above ÷. To return to the normal display, simply press the ON/CE key.
Q: What batteries does the HP 20b use, and how do I replace them?
A: The HP 20b takes two, 3-volt CR2032 lithium batteries. The batteries are very easy to change by simply removing the cover on the back side of the calculator. You will need a very small (eyeglass repair kit size) Phillips head screwdriver as the battery edges are secured by screws, at least on mine. Place the batteries with the positive (+) side up.
Q: How do I enter a negative number into one of the TVM keys on the HP 20b?
A: The way to do it is by using the +/- (change sign) key. For example, to enter -1,000 into FV, press 1000 +/- FV.
Q: How do I change the HP 20b so that it uses RPN data entry instead of algebraic (or vice versa)?
A: First, many people aren’t familiar with RPN and therefore often don’t know that most calculators use algebraic data entry. So, think of algebraic as “normal calculator” mode. RPN is a very different (and, I would argue, far superior) method of data entry — it makes life much easier when entering equations. In any case, if your 20b is in the wrong mode you can fix it by pressing Mode and scrolling down (5 times) until you see Chain, Algebraic, or RPN on the screen. Simply press INPUT until you see RPN. Now press ON/CE to return to normal operation. If you chose RPN, you will see an indicator on the far right side of the screen.
Q: How do I enter dates on the HP 20b?
A: The 20b supports two date entry formats: MM.DDYYY or DD.MMYYYY. MM stands for the month (1 = January, 11 = November, etc), DD stands for the day of the month (02 for the second and so on), and YYYY stands for the year. The default is MM.DDYYYY. To change this, press Mode and then scroll down (2 times) until you see a date format on the top line. Press INPUT to switch between the formats, and ON/CE once you have made your selection.
If the date that you wish to enter is September 25, 2010 then you would type either 9.252010 or 25.092010, depending on the format that you are using.
Q: How do I reset the HP 20b to its factory default settings?
A: You should almost never need to do this, but if the calculator starts doing odd things it is worth a try. For example, somebody asked my why their 20b was giving truly bizarre answers to a simple time value of money question. I didn’t know and suggested a reset and it fixed the problem.
Resetting the calculator is easy: Turn off the calculator. Now, hold down the ON/CE key while you simultaneously press the keys at both ends of the top row (far left and far right). In other words, hold down those three keys simultaneously: ON/CE N Amort. If you do it right, the calculator should display “ALL RESET” on the screen. Press INPUT to give the go-ahead, and then ON/CE to return to normal operation. Note that you will now need to redo any customized settings that you may use. For example, you may need to set the calculator to RPN mode (if you use that instead of algebraic), set the payments per year to your preferred number (I always use 1, but the factory default is 12), and reset the number of decimal places that are displayed on the screen.
You can also reset the calculator by pressing 🠄 (Reset) and scrolling down (10 times) until you see ALL on the screen. If you now press INPUT you will be prompted with Del.All? and you would press INPUT to do the reset.
Finally, if you remove the back cover you will see a tiny hole labeled “Reset” in between the batteries. I haven’t tried it, but if you insert a paper clip into that hole it should reset the calculator. I would only try this if the other two methods don’t work.
Q: How do I find roots other than square roots using the HP 20b?
A: In finance it seems that we are forever calculating various roots (cube root, fourth root, 365th root, etc). Fortunately, this is pretty simple to do if you can remember a simple mathematical rule:
$$\sqrt[N]{X} = {X^{\frac{1}{N}}}$$
So, to calculate the 5th root of 100, we simply raise 100 to the 1/5th power. To do this on the 20b type: 100 yx 5 1/x =. In this example, the 5th root of 100 equals 2.51189. Note that yx is the shifted function of the 3 button, and 1/x is the shifted function of the – button. Using this technique you can calculate any root.
Q: My calculator only has a key to calculate natural logarithms. How do I calculate logarithms to other bases (say, base 10)?
A: Most often, in finance, we use natural logarithms (base e), usually abbreviated as Ln(x). However, sometimes we need to use other bases. Converting from base e to any other base can be done with the following formula (I’m converting to base 10):
$$Lo{g_{10}}\left( X \right) = \frac{{Ln\left( X \right)}}{{Ln\left( {10} \right)}}$$
So, just calculate the natural log of your number, and then divide it by the natural log of the new base. For example, Log10(3) = Ln(3)/Ln(10) = 0.47712.
If you need a base 10 (common) logarithm, you can do that by using the Math button. For this example, you would press 3 Math and then scroll down until you see LOG in the top line. At that point press INPUT ON/CE and you will now see 0.47712, which is the correct answer.