How to Enter and Read E-Notation on the Casio fx-991 Calculator

E-notation is the compact scientific-notation display used by Casio fx-991 series calculators. This reference explains how to enter and read it while preserving significant figures and rounding discipline. For broader rules, see our Scientific Notation and Significant Figures guides.

Rule Statement

On Casio fx-991 calculators, a number in E-notation is displayed as m E n, meaning m × 10ⁿ. The coefficient m is normally in the range 1 ≤ |m| < 10 for scientific notation; the exponent n is an integer. The E is not Euler’s number. To enter, key the coefficient, press ×10^x or EXP, key the exponent, then press =. Negative exponents require the (-) key. All digits shown in the coefficient are significant unless the display is in a fixed-decimal mode.

Reading rule: treat 1.234E5 as 1.234 × 10^5. The exponent is exact; the coefficient carries the measurement precision. See Sig Figs in Scientific Notation.

Visual/Digit Map

Display anatomy for 6.022E23:

Keypad map: ×10^x or EXP inserts the E; (-) makes a negative exponent; ENG converts to engineering notation; S⇔D toggles decimal/fraction display.

Worked Examples

Example 1: Entering 6.022 × 10^23

1. Press 6 . 0 2 2.
2. Press ×10^x or EXP. Display shows 6.022×10^ or 6.022E.
3. Press 2 3.
4. Press =. Display: 6.022E23.

Read as 6.022 × 10^23. The coefficient has four significant figures.

Example 2: Entering 4.5 × 10^-4

1. Press 4 . 5.
2. Press ×10^x or EXP.
3. Press (-) 4. Do not use the subtraction − key.
4. Press =. Display: 4.5E-4.

Example 3: Converting 12345 to E-notation

Enter 12345. Press =. If display is decimal, press S⇔D or use ENG to cycle. Scientific E-notation: 1.2345E4. Engineering notation: 12.345E3. Both represent the same value; the exponent convention differs. See Engineering Notation.

Example 4: Significant figures in 1.20E2

1.20E2 = 1.20 × 10^2 = 120, but with three significant figures. The trailing zero is significant because it is written in the coefficient. If the measurement only justified two significant figures, write 1.2E2. This is why E-notation removes ambiguity in trailing zeros. See Ambiguous Trailing Zeros.

Counter-Examples

• E as Euler’s number: 1.23E4 is not 1.23 × e × 4. It is 1.23 × 10^4 = 12,300.
• Wrong negative key: Pressing − instead of (-) for 4.5E-4 can cause a Syntax ERROR or unintended subtraction.
• Ignoring addition rule: 1.2E2 + 3.45E2 = 4.65E2 on the calculator, but if 1.2E2 has its last significant digit in the tens place, the sum should be rounded to the tens place: 4.7E2. See Addition and Subtraction.
• Double rounding: Rounding 1.23456E3 to 1.23E3 and then to 1.2E3 is not the same as rounding the original directly to 1.2E3. Avoid intermediate rounding.
• Assuming display precision equals internal precision: The fx-991 series typically carries 15 internal digits but displays 10. A displayed 1.234567891E10 may hide guard digits.

Convention Comparison Table

Standards Citation

ISO 80000-1:2009, Quantities and units — Part 1: General, Clause 7.3.3, specifies that numerical values may be expressed as a number between 1 and 10 multiplied by a power of 10. NIST SP 811, §7.7, gives the same convention for SI scientific notation. ASTM E29-22, Sections 6–7, provides standard practice for using significant digits and rounding in test data. The GUM (JCGM 100:2008), Clause 7.2.2, advises against excessive digits when reporting estimates and uncertainties. This site’s significant figures calculator applies these rules automatically.

Common Mistakes

1. Reading E as ‘e’ (2.718…). E is an exponent marker only.
2. Using the wrong minus key. Use (-) for negative exponents.
3. Dropping significant zeros. 1.200E3 has four sig figs; 1.2E3 has two.
4. Applying multiplication/division sig-fig rules to addition. Addition uses decimal places, not total sig figs.
5. Rounding before the final step. Keep full internal precision, then round once.
6. Confusing ENG and SCI modes. ENG forces exponents to multiples of 3; SCI uses 1 ≤ |m| < 10.
7. Assuming all calculators use the same E key. On Casio fx-991, it is ×10^x or EXP; on TI-84, it is 2nd EE.

Quick Reference Table

Related Rules

• Scientific Notation
• Engineering Notation
• Significant Figures
• Rounding Rules
• Multiplication and Division
• Addition and Subtraction
• Sig Figs in Scientific Notation

Precision note: E-notation is not merely a display convenience. It is a precision statement. The coefficient tells you what is known; the exponent tells you the order of magnitude. Always report the same number of significant figures as your measurement justifies.