Sunday, September 14, 2014

Retro: Casio fx-115D SUPER-FX

I recently purchased two calculators from

* Casio fx-115D SUPER-FX and
* Radio Shack EC-4004 (I'll talk about this in another post).

Date the fx-115D SUPER FX was first manufactured: about 1995, according to (

I honestly thought this model was around in the late 1980s or early 1990s. Hard to tell when Casio does not date their user manuals.

As with most solar-powered calculators, the fx-115D SUPER FX (herein referred to as fx-115D from this point forward) has a battery backup. This means we can store data and it will be retained after the calculator is turned off.

In addition to the independent memory (M), the fx-115D has six additional memory registers. The Kin key stores the number into one of the six registers, which the Kout key is the recall key. Better yet, the fx-115D supports storage arithmetic.

Storage Arithmetic:

Let # represents registers 1 through 6:

Add x to #: x [ Kin ] [ + ] #
Subtract x from #: x [ Kin ] [ - ] #
Multiply x to #: x [ Kin ] [ × ] #
Divide #/x: x [ Kin ] [ ÷ ] #

Constant arithmetic operation keys are executed by pressing the arithmetic key twice. Then enter each operand then the equals key. I wonder if anyone used this feature? Here are the procedures for constant arithmetic operation:

Addititon: x + a, x + b, etc...
x [ + ] [ + ] a [ = ], b [ = ], repeat

Subtraction: a - x, b - x, etc...
x [ - ] [ - ] a [ = ], b [ = ], repeat

Multiplication: x * a, x * b, etc...
x [ × ] [ × ] a [ = ], b [ = ], repeat

Division: a/x, b/x, etc...
x [ ÷ ] [ ÷ ] a [ = ], b [ = ], repeat

Other features include:

* Complex Numbers. This is unique for the time as complex numbers were the imaginary parts were entered with a [ i ] key (actually Kin and Kout were deactivated in this mode) instead of the a and b keys. Available functions in complex numbers: arithmetic, 1/x, absolute value, and argument. Powers, logarithms, and trigonometric functions worked only on real numbers.

* Engineering Mode. The shift of the number keys allowed the user to enter an engineering prefix (nano-, micro-, etc...).

* Single Variable statistics

* Linear Regression

* Base Mode with conversion, with Boolean functions AND, NOT, OR, XOR, and XNOR. The [ 1/x ] acts like a negation key, but I am not sure it is 1's or 2's compliment. The manual doesn't state.

* Fractions, complete with mixed/proper fraction conversion. The decimal/fraction works to, if you initially enter a fraction.

* ENG and <-ENG key. These represent a number in different ways:

ENG: decreases the exponent part by 10^3, multiplies the mantissa by 1000
<-ENG: increases the exponent part by 10^3, divides the mantissa by 1000

Example: 23400 [ = ]
[ ENG ] (23.4 x 10^3)
[ ENG ] (23400 x 10^0)
[ ENG ] (23400000 x 10^-3)

23400 [ = ]
[ <-ENG ] (0.0234 x 10^6)
[ <-ENG ] (0.0000234 x 10^9)
[ <-ENG ] (0.0000000234 x 10^12)

These keys are still present on Casio non-graphing calculators, including the entry level fx-260 Solar.

The operating system is AOS (Algebraic Operating System). I realize that AOS is a Texas Instruments term, but it applies here. Simply put, any one-argument function (e^x, trig, log) are pressed after the number is entered. Example:

ln 2431.74 is calculated as 2431.74 [ ln ] (Result: 7.796362329)

Another calculator that I had fond memories of is now back in the collection.


This blog is property of Edward Shore. 2014


  1. Ha, what a coincidence! The fx-115D was the first scientific calculator I ever got, and the fx-115ES Plus is the one I'm using now.

    By the way, the fx-115D certainly was around before 1995. I got mine in 1993, from Germany, so is off by at least 2 years.

  2. Eddie, to be clear, you cannot enter:
    cos45 + isin45
    into the fx-115D calculator?

    1. Lonewolf(TM),

      Here is one way to do it. First, enter Complex mode by pressing [MODE] [EXP]. Then:

      45 [cos] [ + ] 45 [sin] [ x ] [Kin](i) [ = ]

      Press [ > ] to switch between the real and imaginary part of the complex number.


    2. Amazing Eddie Shore! --now I am going online to try and find one to buy (to replace my other one-line always-carry Casio fx-260).

      Were it not possible to input the trigonometric form of a complex number on the fx-991D, I would have passed on buying one online. Thank you.
      /Silicon Valley Regards

  3. Ed, I need manual pdf for 115d
    Mine have blank pages

    1. Mladen:

      You can try this page:

      I admit this is not the most detailed manual ever, it is only a quick guide.


  4. This comment has been removed by the author.


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