Look for a DEG/RAD indicator near the top of the display and tap it (or press the MODE key on hardware calculators) to toggle. Use DEG for geometry, navigation, and most homework problems where angles are given in degrees; use RAD for calculus, physics, and anywhere angles appear inside derivatives, integrals, or unit circle work. The current mode applies to sin, cos, tan and their inverses.

Use the EE or EXP key (sometimes labeled ×10ˣ). Type 6.022, press EE, then 23 — the display shows 6.022E23, which the calculator treats as 6.022 × 10²³ internally. Typing 6.022 × 10 ^ 23 works for moderate exponents but can lose precision near the calculator's exponent limits, so EE is preferred for very large or very small numbers.

Standard PEMDAS / BODMAS: parentheses first, then exponents and roots, then multiplication and division left to right, then addition and subtraction. Implicit multiplication next to parentheses, like 2(3+4), is treated as 2 × (3+4) = 14. When an expression is ambiguous — 1/2x is the classic example — add explicit parentheses to force the intended grouping.

Calculations follow the IEEE 754 double-precision floating-point standard, giving roughly 15-17 significant decimal digits. Results displayed with fewer digits are rounded for readability. Tiny artifacts such as sin(180°) showing 1.2 × 10⁻¹⁶ instead of exactly 0 come from the binary representation of irrationals like π, not from a calculation mistake.

Use a scientific calculator whenever a problem involves trigonometry, logarithms, exponents beyond squares, roots beyond square roots, scientific notation, or expressions with nested parentheses. Four-function calculators evaluate strictly left to right and ignore operator precedence, so they give wrong answers for anything more complex than simple arithmetic.

Three limits matter in practice. First, overflow: numbers larger than about 1.8 × 10³⁰⁸ return Infinity. Second, underflow: numbers smaller than about 5 × 10⁻³²⁴ collapse to 0. Third, catastrophic cancellation: subtracting two nearly equal large numbers can wipe out most of the significant digits, so rearrange formulas (for example, use 1 - cos(x) ≈ x²/2 for small x) when high precision matters.