**Retro Review: Casio fx-19**

**Quick Facts**

Model: fx-19

Company: Casio

Production Years: 1976 - 1977

Power: 4 AA batteries. AC adopter is available.

Type: Scientific

Operating System: Chain

Memory Registers: 1

Display: One line: 8 digits or 5 digits with 2 digit exponent (10^xx)

**Features and Keyboard**

This is an early Casio scientific calculator with a standard set of features:

* logarithm, antilogarithm (base 10 and e)

* trigonometry

* fractions (auto simplification)

* one variable statistics

The fx-19 has 38 keys with two switches: one for power and one for mode selection. The mode selection switch has three angle modes (radians, degrees, grads) and one variable statistics (S.D σ).

There is only one shift button, [ arc ], which is only for the inverse trigonometric functions arcsin, arccos, and arctan.

Everything is displayed in floating point mode.

**Statistics Mode**

In statistics mode, a lot of the keys are repurposed:

[ AC ]: clear all statistical data

[ = ]: enter statistical data

[ ° ' '' ] ( σn ): population deviation

[ 1/x ] ( σn-1 ): standard deviation

[ MC ] ( x-bar ): mean

[ MR ] ( n ): number of data points

[ M- ] ( Σx ): sum of data points

[ M+ ] (Σx^2 ): sum of the square of data points

Example:

Data Set: { .786, .869, .542, .599, .649 }

In SD mode,

[ AC ] .786 [ = ] .869 [ = ] .542 [ = ] .599 [ = ] .649 [ = ]

[ ° ' '' ] ( σn ): 0.120928

[ 1/x ] ( σn-1 ): 0.1352017

[ MC ] ( x-bar ): 0.689

[ MR ] ( n ): 5

[ M- ] ( Σx ): 3.445

[ M+ ] (Σx^2 ): 2.446723

**Chain Mode**

As we can tell from the pictures, there are no parenthesis keys. The calculator operates in chain mode, which means the order of operations are not followed.

In the following examples, the Degrees mode is set.

Examples:

8 [ × ] 5 [ + ] 11 [ = ] returns 51

5 [ + ] 8 [ × ] 11 [ = ] returns 143

For complex calculations, often the use of the memory keys [ M+ ], [ M- ], [MR], and [ MC ] are needed. Unfortunately, there is no indicator whether a non-zero number is in memory. Hence, checking with the [ MR ] key is needed.

Like many four-function regular calculations, [ M+ ] and [ M- ] complete pending operations.

Examples:

71 × 27 + 28 × 16 - 39 × 14

[ MC ]

71 [ × ] 27 [ M+ ]

28 [ × ] 16 [ M+ ]

39 [ × ] 14 [ M- ]

[ MR ]

Result: 1819

sin(30 + 0.05) / sin(30 - 0.05)

In division rational expressions, I prefer to tackle the denominator first.

[ MC ]

30 [ - ] .05 [ = ] [ sin ] [ M+ ]

30 [ + ] .05 [ = ] [ sin ] [ ÷ ] [ MR ] [ = ]

Result: 1.0030275

**The Power Key**

The power key [ x^y ] requires two arguments, the base (x) and the exponent (y). When the power key is first press, the natural logarithm of x is displayed.

8^5

8 [ x^y ] (Display: 2.0794415)

5 [ = ] (Display: 32768)

The user of the power key is a treated as a separation calculation. If we press any function for x, the power is canceled out.

6^(log 2)

Incorrect way:

6 [ x^y ] 2 [ log ] [ = ]

Result: 0.30103 (log 2)

Correct way:

[ MC ] 2 [ log ] [ M+ ]

6 [ x^y ] [ MR ] [ = ]

Result: 1.7149319

The exception is roots, x [ x^y ] y [ 1/x ] [ = ]

7^(1/5)

7 [ x^y ] 5 [ 1/x ] [ = ]

Result: 1.4757732

**Final Thoughts**

The fx-19 is a classic calculator, and is a good option for those who want both a scientific calculator but operates more like a four-function calculator. The fx-19 is still relatively available.

**Source**

"Casio fx-19" calculator.org.

https://www.calculator.org/calculators/Casio_fx-19.html

Retrieved October 1, 2023

Eddie

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