### Why your calculator may be giving you the wrong answers?

- Data Entry Error: a common mistake is in entering one number incorrectly, or in forgetting a step such as entering 0 in FV or PMT for certain calculations (which means that whatever number is in the key from the previous calculation will remain in the key’s memory). You can always check what is stored in any particular key by pressing RCL and then the key. For example, to check what is in the PV key, you can press RCL PV If you get a number that doesn’t make sense or is wrong, you can simply change this one number rather than starting again from the beginning. RCL can be used to figure out where a data entry problem occurred.
- BEGIN appears on your calculator screen: if your calculator shows BEGIN on the bottom of the screen, you will get the wrong answers in most financial calculations. Mortgage payments are made in arrears or “not in advance” (i.e., you pay interest at the end of each month), compared to lease payments which are made in advance (i.e., you pay on the 1st of each month for the month ahead). You should set your calculator to “end-of-period” mode by pressing shift (the yellow key) BEG/END. This will remove BEGIN from your screen.
- Decimal Places: the HP 10B/10BII calculator will display 0 - 10 decimal places. If you have the calculator set to show, say, 2 decimal places, it will automatically round off answers to the nearest cent. You don’t want this setting because some calculations require a lot more accuracy and in others you need to be able to decide rounding for yourself. You should put your calculator in “floating decimal” mode which shows the most significant decimals possible – press shift DISP .{period}
- Batteries: if the batteries are dying, your calculator screen will dim and eventually a little battery symbol will show in the bottom right corner. However, your calculator won’t start to give wrong answers as the batteries run out! See your HP 10B/10BII owner’s manual for instructions on how to replace the batteries.
- Self-test: if none of the above solves the problem, you can test the calculator using its self-test feature. If your calculator fails the self-test, before concluding it is defective, try running the self-test several times. It should come up with the same error message consistently - if it does not, then it is unlikely to be malfunctioning.