TI-15: Memory and Hidden Memory Arithmetic

TI-15:  Memory and Hidden Memory Arithmetic

Many thanks to Bob Patton, a fellow HP calculator enthusiast, who sent me this information.  One of the door prizes I won from HHC 2016 was a TI-15 calculator which Patton donated.  (I also previously purchased an HP 32 SII). 

A link to my previous retro review (October 2016):  http://edspi31415.blogspot.com/2016/10/review-texas-instruments-ti-15.html

Storing Numbers in Memory: A Unique Way

I don’t think I ever seen this storage sequence like the one that is presented in the TI-15.  Almost all calculators have a sequence as such:  ([2^nd/Shift]) [ STO ] ([register/variable]).  However to store numbers in memory on the TI-15, the sequence is [ = ] [ >M ] [ = ].

For example, to store 100 in memory, I would press 100 [ = ] [ >M ] [ = ].

To recall numbers from memory, press [MR/MC].  If this key is pressed twice, the memory is cleared.

Hidden Talent: Memory Arithmetic

Patton sent me the information of this neat undocumented feature of memory arithmetic.  The following sequences are:

[ = ] [ M> ] [ + ]:  Add number to memory M

[ = ] [ M> ] [ - ]:  Subtracts number from memory M

[ = ] [ M> ] [ * ]:  Multiplies number to memory M

[ = ] [ M> ] [ ÷ ]:  Division,  M ÷ number

[ = ] [ M> ] [ Int÷ ]: Integer Division,  int(M ÷ number)

Press [MR/MC] to recall the result.

Example

Store 100 to memory: 

100 [ = ] [ >M ] [ = ]

Add 10 to M.  (Result: 110)

10 [ = ] [ >M ] [ + ]

Subtract 10 from M.  (Result: 100)

10 [ = ] [ >M ] [ - ]

Multiply 10 to M.  (Result:  1,000)

10 [ = ] [ >M ] [ * ]

Divide M/10.  (Result:  100)

10 [ = ] [ >M ] [ ÷ ]

Integer Division.  Int(M/6) (Result:  16)

6 [ = ] [ >M ] [ Int÷ ]

Special thanks to Bob Hutton!

Eddie

This blog is property of Edward Shore, 2017.

Review: Texas Instruments TI-15

Review: Texas Instruments TI-15

Website:  https://education.ti.com/en/us/products/calculators/elementary-calculators/ti-15-explorer/tabs/overview#tab=specifications

Production:  Since 2000

Power: Solar with CR2025 backup

Price: Depending on where you shop, $14-$22. I won one as a door prize. 

I won a TI-15 as a door prize (among a Raspberry Pi Zero and HP 49G) on HHC 2016.   

A Curious Calculator 

This is a curious calcualtor, destined for elementary school students.  More advanced than a regular four-function calculator yet it isn't a scientific calculator.  To start, the TI-15 operates algebraically, like most scientific calcualtors.  That is, you enter an expression, press [ Enter = ], using the order of operations.  The TI-15 also features a power key [ ^ ], a pi key [ π ], and set a fraction keys.  Furthermore, pressing [ π ] inserts the π the character instead of its approximation (3.141592653590).  Any results in the form of n * π, where n is an integer (like 3 π ) as such.  Converting answers to their decimal approximation will require pressing the [ F <-> D ] key. 

For something really unique, try the [>%] key. It converts decimals to percent form (0.19 to 19%). 

Fractions 

Fractions are a major feature of the TI-15.  Entering fractions require entering the part number and the appropriate button indicate which part to be entered.  For example: to enter 3 1/4, press 3 [Unit] 1 [n/] 4 [/d].  The entire two-line screen is used to display fractions.  Fractions can be simplified, converted to decimal approximation, and conversions between mixed and improper forms are available.  After simplifying the fraction, you can press [Fac] to display the factor used to simplify fractions. 

For example, enter 105/220.  Assume that manual simplification mode is set.  105 [n/] 220 [/d] [ Enter = ]. Press [Simp] [Enter=] to get 21/44. Pressing [Fac] returns 5, meaning a factor of 5 was used to reduce 105/220 to 21/44. 

Programming?

The TI-15 is programming calcualtor.  Well, sort of. The two programming keys [Op1] and [Op2] allows for storing a single operation (+, -, *, ÷, Int ÷ , ^) and single number operation.   Testing the TI-15, I couldn't get it work beyond this limitation. 

Place Value

Results can be rounded to 3 decimal places by pressing [Fix], then [1], [0.1], [0.01], [0.001] for 0, 1, 2, or 3 places respectively.  That is not surprising.  However, this might be one of the few calculators (if not only) to a round to tens, hundreds, or thousands mode. 

Problem Solving and Quiz

The elementary calculator has a quiz mode with three difficulty levels of basic arithmetic.  You can also write your own problems, replacing a number or operation with a ?, and try to quiz yourself.  

Review: The Verdict

The TI-15 is available only online (that I know of). I think it is an interesting and curious calculator to add to the collection, and can be enjoyable for those who want more options but are intimidated or don't desire by scientific calculators.  The keyboard is nice and big, I wish the screen was bigger but it is very readable. 

I wish the basic four-function calculators would consider adding a π and power button to their calculators.  If you want a TI-15, shop around.  

Eddie

This blog is property of Edward ashore.