Retro Review: Casio fx-991H
Quick Facts:
Model: fx-991H
Company: Casio
Years: My guess would be the late 1980s-early 1990s
Memory Register: 1 independent memory, 6 registers
Battery: Solar with battery back up (GR927)
Display: 10 digits, 2 digit exponent
Logic: Algebraic
The fx-991H works best when in full or almost full light.
Features
The fx-991H is similar to the fx-115D SUPER FX except:
* The fx-991H has 32 built in scientific constants, based on ISO Standards of 1980 and (Japan Industrial Standards) of 1985. Trust me, most values of the scientific constants do not change much.
* The fx-991H has a hard case cover instead of the pocket cover. Personally, I like the hard case.
I also like the feel of the keyboard, I can feel definite clicks when I press the buttons.
Here is a quick run down what you get with the fx-991H:
* Six additional registers through Kin/Kout. Kin is the shifted command of the [ Kout ] key. Storage arithmetic is permitted (yay!). For registers 1 through 6:
Addition: x [ SHIFT ] ( Kin ) [ + ] K#
Subtraction: x [ SHIFT ] ( Kin ) [ - ] K#
Multiplication: x [ SHIFT ] ( Kin ) [ × ] K#
Division: x [ SHIFT ] ( Kin ) [ ÷ ] K#
* Constant arithmetic. To use it, the arithmetic key must be pressed twice.
Addition: x [ + ] [ + ] a [ = ], b [ = ], .... for a + x, b + x, ....
Subtraction: x [ - ] [ - ] a [ = ], b [ = ], .... for a - x, b - x, ....
Multiplication: x [ × ] [ × ] a [ = ], b [ = ], .... for a * x, b * x, ....
Division: x [ ÷ ] [ ÷ ] a [ = ], b [ = ], .... for a / x, b / x, ....
* Percent Function, [ SHIFT ] [ = ] ( % ). This percent function operates like a lot of the Casio basic calculators.
What is n% of y? y [ × ] n [ SHIFT] [ = ] ( % )
What is percent portion of part n of total y? n [ ÷ ] y [ SHIFT ] ( % )
Percent difference from n to y? n [ - ] y [ SHIFT ] ( % )
Add n% to y: y [ × ] n [ SHIFT ] [ = ] ( % ) [ + ]
Subtract n% from y: y [ × ] n [ SHIFT ] [ = ] ( % ) [ - ]
Find the percent ratio of (n + y)/y: n [ + ] y [ SHIFT ] [ = ] ( % )
* Engineering Mode, where all answers are displayed in the form of x ee,
(x * 10^ee, ee is a multiple of 3). We also have use of engineering constants (M for mega, G for giga, T for tera, etc.)
* Base Conversions with Boolean functions. The standard set of functions are present (AND/NOT/OR/XOR/XNOR/NEG) with the standard set of bases (HEX/DEC/OCT/BIN)
* Statistics with Linear Regression.
A = constant term (y-intercept)
B = regression coefficient (slope)
r = correlation
y = A + Bx
* Complex Mode. Complex mode is limited to arithmetic, independent variable storage, argument, absolute value
* Fractions. Simplification is automatic.
* Decimal/DMS conversions. Convert all numbers in DMS (degrees-minutes-seconds) to decimals before operating.
* Hyperbolic functions.
* Scientific Constants. There are 32 scientific constants, accessed through the [ CONST ] key or the [ SHIFT ] [ CONST ] key combination. Constants are stored in the keys 0-9, ., EXP, +, -, ×, ÷.
Examples:
Speed of Light, [ CONST ] [ 1 ]: 299792458 m/s
Earth's Gravity Constant, [ CONST ] [ + ]: 9.80665 m/s^2
Universal Gravity Constant, [ CONST ] [ 3 ]: 6.672 * 10^-11 N m^2/kg^2
Fine-Structure Constant, [ SHIFT ] [ CONST ] [ 3 ]: 7.2973506 * 10^-3 (unitless)
Stefan-Boltzmann Constant, [ SHIFT ] [ CONST ] [ × ]: 5.67032 * 10-8 W/(m^2 K^4)
For a full list of the 32 constants:
https://drive.google.com/file/d/1r0OP-R9wddhqo0xrsQfL26eJx8FkNolD/view?usp=sharing
I checked with the manual to be sure that these are constants and it checks out.
Closing Thoughts
I really like this keyboard. It is clean and the keys are very responsive. The display is sharp. I am happy to add this calculator to the collection. Prices vary, I think I got mine for about $13 U.S., but I have seen prices on the internet go as high as $40 U.S.
I like how Casio puts a lot of features and makes calculators more affordable. This is a good brand to consider if you need to get the most bang for your buck. You also get good quality of calculator.
If you want to see my review of the fx-115D SUPER FX from 2014:
http://edspi31415.blogspot.com/2014/09/retro-casio-fx-115d-super-fx.html
Until next time,
Eddie
All original content copyright, © 2011-2022. Edward Shore. Unauthorized use and/or unauthorized distribution for commercial purposes without express and written permission from the author is strictly prohibited. This blog entry may be distributed for noncommercial purposes, provided that full credit is given to the author.
