The TI-84 Plus CE is permitted on most sections of the SAT and the entire ACT mathematics section. It is faster than hand calculation when used correctly. It is slower and less accurate when used incorrectly — and the errors it introduces are often not obvious, which is why they cost more points than arithmetic mistakes.
Mistake 1 — Wrong angle mode
The TI-84 operates in either degree or radian mode. The default after a reset is radian. sin(30) in radian mode returns −0.988, not 0.5.
Check the mode before every exam: press MODE, verify that "DEGREE" is highlighted. The current mode displays in the top-left corner of the home screen (D for degree, R for radian).
SAT trigonometry problems sometimes specify radians explicitly and sometimes use degrees. Read the problem. ACT problems use degrees unless stated otherwise.
Mistake 2 — Order of operations with fractions entered as division
Entering 3 + 5 / 2 on the home screen gives 5.5, not 4, because the calculator applies PEMDAS correctly and evaluates 5/2 = 2.5 before adding 3.
To evaluate (3+5)/2, enter it as (3+5)/2 — with the parentheses. The fraction notation on the TI-84 (accessible via ALPHA + Y= to open templates) handles this correctly, but requires more keystrokes.
Mistake 3 — Rounding stored values
If you compute a value, round it to two decimal places, write it down, and type it back in for the next calculation, you introduce rounding error that compounds. The correct approach: store the exact result in a variable (press STO→, then a letter key) and use the variable in subsequent calculations.
Mistake 4 — Using ENTER instead of EXE for a chain of calculations
On the home screen, pressing ENTER executes the expression and clears it from the input line. Students who need to modify an expression slightly often retype it from scratch. Use the up arrow after pressing ENTER to retrieve the last expression, then use the left/right arrows to edit.
Mistake 5 — Forgetting that √ only covers the next character without parentheses
2nd + √ enters a square root symbol. If you type √2 + 3, the calculator computes √2 + 3 ≈ 4.414. If you want √(2+3) = √5 ≈ 2.236, you must type √(2+3). The calculator shows the radical sign extending over the entered expression, which often makes this error visible — look at the screen carefully.
Mistake 6 — Using the subtraction key for negation
The minus sign (−) key is for subtraction: it requires a preceding number. The negation key (−) on the bottom row of the keypad is for making a number negative. Typing − 5 when you mean negative 5 requires the negation key, not the subtraction key. Many TI-84 errors with negative exponents trace to this.
Mistake 7 — Not clearing lists before statistical calculations
If you use the calculator for statistics (computing means, standard deviations, regression) and there is leftover data in L1 or L2 from a previous problem, the calculator includes that data in any list-based computation. Clear all lists before entering new data: press STAT → ClrList → 2nd+1 (L1), ENTER.
Frequently Asked Questions
Is the TI-84 allowed on the digital SAT?
Yes. The digital SAT (College Board's current format) provides a built-in Desmos graphing calculator on-screen, and also permits an approved physical calculator including the TI-84 Plus CE. Practice with whichever you plan to use.
Does the ACT specify which calculators are permitted?
The ACT permits four-function, scientific, and graphing calculators but prohibits specific models with computer algebra systems (CAS), including the TI-89, TI-92, and TI-Nspire CAS. The TI-84 Plus CE is permitted.