Texas Instruments TI-81 scientific calculator

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The calculator.

Brand name Texas Instruments
Model number TI-81

Picture of TI-81 keyboard [link opens in new window]. (Provided by the author of this page.)

Logic system. Does your calculator use algebraic or RPN (reverse Polish notation) logic? How do you tell? An algebraic calculator has an = key; An RPN calculator has an ENTER key. To add two numbers (say, 2 & 3) on an algebraic calculator, you type the keys "2 + 3 =". On an RPN calculator, you type "2 ENTER 3 +".
Algebraic or RPN? Algebraic
Algebraic calculators can be further subdivided into AOS and DAL. If you know which type yours is, you can write that here. Otherwise, you will figure that out later on the form. DAL

Shift keys. Shift keys are used to get the second (or third) function for a particular key. If there are two shift keys, list both.
What is the label on the "shift" key(s) 2nd
Where is the shift key? top left

Scientific notation; entering. Identify the key used to enter the exponent. (It is usually EE or EXP, or similar.)
* A special case concerns entering a number that starts with 1x in scientific notation: do you need to enter the 1? Try it... Calculate 1x1012 * 2. Do it twice, once with the first 1 and once without it. Do you need to enter the 1 to get the correct answer, 2x1012?
* The key for making an exponent negative is the same key used for entering negative numbers.

What is the label on the key for entering exponents? EE
Where is that key? middle, above 7
When entering a number that starts with 1x in scientific notation, do you need to enter the 1? (e.g., 1x1012) No; ok to just enter EE 12
What is the key for making an exponent negative? (-)
Where is that key? bottom row, next to ENTER

Scientific notation; display.

Most scientific calculators allow you to "force" the display to use (or to not use) scientific notation.

Many calculators allow you to set the number of decimal places displayed.

(Some calculators also have an option for "Engineering notation", which is a variation of Scientific notation. Not important for most people.)
Scientific notation is turned on switching the "MODE" from "Norm" to "Sci". Press the MODE key (second row from top) and use the arrow keys to move the highlight from "Norm" to "Sci". Finish setting by pressing ENTER, then CLEAR.
To force ordinary decimal notation, use the same procedure, but choose "Norm".

To set the number of decimal places in the display:
Also from the MODE key, you can select "Float" or a digit (0-9) for the number of decimal places. Finish setting by pressing ENTER, then CLEAR.

Logarithms (and anti-logs). In intro chem we most often use base 10 logs (log10), for example with pH. The log10 is the power of 10 of the number. For example, the log10 of 1000 is 3; and then the antilog10 of 3 is 1000.
* On some calculators, you press the LOG key before the number, and on some you press the number then the LOG key.

How is the log10 key labeled? LOG
How is the base 10 antilog key labeled? 10x (blue).
It is 2nd-shift LOG.
To take the log10 of 1000 which do you enter first, the number or the LOG key? LOG.
That is, enter LOG 1000.
The preceding step serves to distinguish AOS and DAL calculators. If your calculator uses algebraic notation, and if you enter the number first, then it is AOS; if you enter the LOG first, it is DAL. The same pattern holds for other one-key functions, such as antilog and square root.

Base e logs (loge or ln) are called natural logs. We do not use these in intro chem, but you are likely to use them if you go much beyond that.
How are the keys labeled for natural logs and antilogs? LN

anti-log: ex.
It is 2nd-shift LN.

Miscellaneous. These are functions we do not use in intro chem, but which you are likely to use in other math and science courses. Briefly noted here.

Angles: degrees or radians

(Some calculators also have an option for "grad". The grad is 0.9 degree, so that a right angle is 100 grad. Not commonly used.)
MODE key.
Down arrow to 3rd row.
Select Rad or Deg.
Press ENTER, then CLEAR
Polar vs rectangular coordinates MODE key.
Down arrow to 7th row.
Select Rect or Polar.
Press ENTER, then CLEAR

You. Please provide your name and e-mail, so I can check back with you if there are questions (and maybe have you proofread the web page for your calculator). We will not list your name at the web site without your explicit permission. We will not make your e-mail available in any case.

May we list your name in the collection (at the web site), to give you credit for providing this information?
If yes, how would you like your name listed? ("handles" ok.)
Ian Frederick-Rothwell

Other notes.
To turn the calculator off: 2nd-shift ON.

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Last update: March 26, 2019