Natural Scientific 991 manual · Chapter 2 of 18

Key by key

Every key on the keypad with what it does on its own, after SHIFT and after ALPHA.

2.1Top row: SHIFT, ALPHA, up and ON#

Key	Primary	After SHIFT	After ALPHA
`SHIFT`	Selects the gold function of the next key.	(cancels SHIFT)	(switches to SHIFT)
`ALPHA`	Selects the red letter of the next key.	(switches to ALPHA)	(cancels ALPHA)
`▲`	Moves up inside a template, or recalls an earlier calculation. Scrolls menus and lists up.
`ON`	Clears the line and answer, like AC.	OFF: does nothing.

2.2OPTN, CALC, arrows and MENU#

Key	Primary	After SHIFT	After ALPHA
`OPTN`	Opens the options menu for the current app (hyperbolic, angle units, Pol, Rec, Int, GCD and so on).	Same as OPTN.
`CALC`	Runs the expression again, asking for a value for each variable.	SOLVE: finds the value of a variable that makes an equation true.	=: types an equals sign.
`◀`	Moves the cursor left, or switches to editing the last answer.
`▼`	Moves down inside a template, or steps forward through history. Scrolls menus and lists down.
`▶`	Moves the cursor right, or steps out of a template box.
`MENU`	Opens the app menu.	SETUP: opens the settings.

2.3Reciprocal, log, fraction, root, square and power keys#

Key	Primary	After SHIFT
`x⁻¹`	Reciprocal: the previous value to the power minus one.	x!: factorial.
`log`	Logarithm template with a base box and a value box.	Σ: summation template.
`/`	Fraction template: numerator over denominator.	Mixed-number template: whole part, numerator, denominator.
`√`	Square root template.	Cube root template.
`x²`	Squares the previous value.	Cubes the previous value.
`x`	Power template: a base with an exponent box.	Root template with a root-index box.

2.4Log, ln, negative, DMS, hyp and sin#

Key	Primary	After SHIFT	After ALPHA
`log`	Base-10 logarithm.	10 to a power.
`ln`	Natural logarithm.	e to a power.
`(−)`	Negative sign for the next number.	∠: separates the modulus and angle of a polar complex number.	Variable A.
`°'"`	Degree, minute, second marks while typing. After an answer, shows it as degrees, minutes, seconds.	← : after a degrees-minutes-seconds answer, switches back to the decimal form.	Variable B.
`hyp`	Opens the hyperbolic function menu.	Abs: absolute value template.	Variable C.
`sin`	Sine.	Inverse sine.	Variable D.

2.5Cos, tan, RCL, ENG and brackets#

Key	Primary	After SHIFT	After ALPHA
`cos`	Cosine.	Inverse cosine.	Variable E.
`tan`	Tangent.	Inverse tangent.	Variable F.
`RCL`	Shows the values of all stored variables.	STO: stores a value in the variable key you press next.
`ENG`	On an answer, moves to the next engineering exponent (a multiple of 3). In Complex it types i.	On an answer, steps the engineering exponent the other way.
`(`	Opens a bracket.	%: percent sign.
`)`	Closes a bracket.	,: comma between arguments.	Variable x.

2.6Integral, S⇔D and M+#

Key	Primary	After SHIFT	After ALPHA
`∫`	Definite integral template with limits.	d/dx: derivative-at-a-point template.
`S⇔D`	Switches an answer between exact form (fraction, root, π) and decimal.	Switches a fraction between mixed and improper form.	Variable y.
`M+`	Adds the answer to memory M.	M−: subtracts the answer from memory M.	Variable M.

2.7The number pad: digits, DEL, AC and operators#

Key	Primary	After SHIFT
`7`	Digit 7.
`8`	Digit 8.
`9`	Digit 9.	RESET: opens the reset menu.
`DEL`	Deletes the character before the cursor.	INS: switches between inserting and overwriting. While overwriting, OVR shows and each character you type replaces the one under the cursor.
`AC`	Clears the line and answer. Backs out of menus and forms.	OFF: does nothing, there is nothing to switch off.
`4`	Digit 4.
`5`	Digit 5.
`6`	Digit 6.
`×`	Multiply.	nPr: permutations.
`÷`	Divide.	nCr: combinations.
`1`	Digit 1.
`2`	Digit 2.
`3`	Digit 3.
`+`	Add.	Pol(: converts x, y to radius and angle.
`−`	Subtract.	Rec(: converts radius and angle to x, y.

2.8The bottom row: 0, point, ×10ˣ, Ans and equals#

Key	Primary	After SHIFT	After ALPHA
`0`	Digit 0.
`.`	Decimal point.	Ran#: a random decimal between 0 and 1.	RanInt#(: a random whole number between two limits.
`×10ˣ`	Times ten to a power. An exponent box follows.	π: the constant pi.	e: the constant e.
`Ans`	Inserts the previous answer.
`=`	Evaluates the line. Also confirms menu choices and form fields.	≈: evaluates and shows a decimal answer.

2.9Moving around menus, forms and tables#

In a menu, press a number to choose that line, or move with ▲ and ▼ and press =.
In a form (the Table setup, Distribution, Equation and Ratio inputs), type a value, press = to accept it and move to the next field, and use ▲ and ▼ to move between fields. The last = runs the calculation.
Press AC to clear a typed field, or to go back one screen.
Result lists with more than four lines scroll with ▲ and ▼.

A form: the Table setup The display shows: f(x)= / Start=1 / End=5 / Step=1. — A form: the Table setup

fx-991EX ClassWiz is a trademark of Casio Computer Co., Ltd.. Trident Calculator is an independent product by South View Studios and is not affiliated with, sponsored by or endorsed by Casio. The name is used only to describe the kind of calculator this model resembles; Trident's names, keys, display, fonts and software are its own clean-room design.