Best FE Exam Calculator 2026: TI-36X Pro vs Casio

Choosing the right calculator for the Fundamentals of Engineering (FE) exam is one of the simplest ways to reduce wasted time on test day. NCEES strictly limits which calculators you can bring into the testing center, so you need to know your options and pick the one that best fits your practice workflow. In this guide, we walk through the approved families, explain why the TI-36X Pro stands out for most FE disciplines, and use our app question tags to show which calculator skills deserve deliberate drilling.

What Calculator Skills Show Up Most?

Across the current FE Test Prep practice library, every app-view question is tagged with the calculator workflow it uses. The June 13, 2026 review scanned 8,872 question rows. These counts are not an official NCEES frequency claim; they are first-party practice-library data that helps you decide which button paths deserve deliberate drilling before test day.

Data note: This table is based on a June 13, 2026 first-party scan of the FE Test Prep practice library. It is not an official NCEES frequency claim, and it should be refreshed after major question-library updates.

Five button paths worth practicing early

Which Calculators Are Approved for the FE Exam?

NCEES publishes an official list of approved calculators that is updated periodically. As of 2026 the approved models come from three manufacturers, identified by model family:

• Casio — any model with fx-115 or fx-991 in its name (e.g. fx-115ES Plus, fx-991CW)
• Hewlett Packard — the HP 33s and HP 35s (both discontinued — don’t buy one new)
• Texas Instruments — any model with TI-30X or TI-36X in its name (e.g. TI-36X Pro)

The same list applies to both the FE and PE exams, so a calculator you buy for the FE is allowed on the PE. The table below compares the models actually worth buying:

Model	Best For	Key Features	Verdict
TI-36X Pro	All disciplines	Polynomial solver, 3×3 matrix ops, linear regression, unit conversions, multi-line display	TOP PICK
Casio fx-991EX	Chemical, Environmental	Spreadsheet mode, equation solver, high-resolution natural display, fast processing	RUNNER-UP
Casio fx-115ES Plus	Budget option	Natural textbook display, complex numbers, basic matrix and vector operations	CAPABLE
TI-30X series	Lightweight backup	Two-line display, fraction simplification, basic scientific functions — no advanced solvers	AVOID

Practice Using Your Calculator — With Exam-Style Questions

Knowing which calculator to buy is step one. Knowing how to use it under exam pressure is what actually moves your score.

The FE Test Prep study app includes Guided Calculator Drills — a dedicated practice mode that teaches the TI-36X Pro’s most exam-critical functions using FE-style and PE-style problems. Open the calculator beside each drill, follow the exact keystrokes, and use the function guide when you need a quick reminder. No generic tutorials. No hunting through videos while you are trying to study.

• Function drills — poly-solv, sys-solv, numeric integration, complex numbers, unit conversions, BASE-N, and more
• Guided walkthroughs — follow the exact key sequence step by step, use the built-in calculator alongside the drill, and learn the traps students hit on exam day
• Discipline-specific tracks — Civil prioritizes systems, surveying trig, and hydraulics conversions; ECE covers complex impedance and BASE-N; Mechanical focuses on fluids, thermo, and hyperbolic functions
• Gotcha checks — targeted drills for order-of-operations traps, mode-switching mistakes, and display-format errors that cause silent wrong answers

The skills lab is part of the full FE Test Prep practice app, available for every FE discipline and selected PE exam tracks.

Try Guided Calculator Drills →

No other calculators are allowed. You cannot bring a graphing calculator such as a TI-84 or TI-89, nor any programmable or CAS-enabled calculator. The proctor at your Pearson VUE testing center will check your calculator before you sit down, and if it is not on the approved list, you will have to take the exam without one.

Frequently Asked Questions

Disclaimer: Always verify the current approved calculator list directly on the NCEES exams page before your exam date. NCEES may update the list at any time, and the information above reflects the list as of this article's publication.

Why Is the TI-36X Pro the Best Choice?

While all of the approved calculators are capable scientific calculators, the TI-36X Pro is widely considered the best option for FE examinees across all disciplines — Electrical & Computer, Civil, Mechanical, and others. The reason is straightforward: it has the most advanced feature set of any calculator on the approved list, and those features align directly with the types of problems you will encounter on the exam.

The Casio fx-115 and fx-991 models are solid calculators and share many of the same capabilities. If you already own one and are comfortable with it, it can certainly get the job done. However, the TI-36X Pro offers a few interface and workflow advantages that make it slightly faster to use under time pressure, which matters when you have roughly three minutes per question.

Our recommendation: Get the TI-36X Pro on Amazon — it is the best investment you can make for your FE exam prep. Buy it early so you have time to practice with the exact keystrokes before exam day.

What Are the Key TI-36X Pro Features for the FE Exam?

Here are the specific features that make the TI-36X Pro invaluable during the FE exam.

Complex Number Mode

Complex numbers appear across FE exam disciplines — from AC circuit analysis (Electrical & Computer) to vibration problems (Civil and Mechanical). The TI-36X Pro lets you enter complex numbers directly, perform arithmetic with them (addition, subtraction, multiplication, division), and convert between rectangular and polar forms with a few button presses. This eliminates tedious manual calculations and dramatically reduces the chance of errors.

Matrix Operations

Linear systems of equations show up across all FE disciplines — from circuit analysis (Electrical) to structural analysis and statics (Civil). The TI-36X Pro supports matrices up to 3x3, allowing you to enter a coefficient matrix, compute determinants, find inverses, and multiply matrices. For a system of three equations with three unknowns, using the matrix solver is far faster and more reliable than solving by hand.

Numeric Solver

The built-in numeric solver lets you enter an equation and solve for any unknown variable. This is useful for problems where you have a known formula but need to isolate a variable that is difficult to rearrange algebraically. Enter the equation, supply the known values, and let the calculator find the unknown. It handles polynomial and transcendental equations alike.

Unit Conversions

The FE exam reference handbook uses SI units, but some problems may present values in other unit systems. The TI-36X Pro has a built-in unit conversion function that covers length, area, volume, temperature, energy, power, pressure, and more. Instead of memorizing dozens of conversion factors, you can let the calculator handle the arithmetic.

Statistics Mode

The statistics mode supports one-variable and two-variable data sets, giving you mean, standard deviation, linear regression coefficients, and correlation. Probability and statistics questions appear on every FE exam discipline, and having these functions readily available saves valuable time.

Vector Calculations

The TI-36X Pro can store and operate on 2D and 3D vectors. You can compute dot products, cross products, and magnitudes directly. This is helpful for statics and dynamics (Civil), electromagnetics (Electrical), and any problem involving force or field vectors.

How Do You Use Your Calculator Efficiently During the Exam?

Having the right calculator is only half the battle. You also need to know how to use it quickly and confidently under pressure. Here are practical tips that can save you valuable minutes on exam day.

1. Learn the key sequences, not just the features. Knowing that your calculator can do complex number math is not enough. You need to be able to switch to complex mode, enter a number in polar form, and convert the result to rectangular form without fumbling through menus. Practice the exact button sequences until they are automatic.
2. Use the multi-line display to check your inputs. The TI-36X Pro shows your entire expression before you press enter. Always glance at the display to verify you entered the right numbers before executing a calculation. Catching a typo before you commit is much faster than redoing a problem.
3. Store intermediate results. The TI-36X Pro has memory variables where you can store values. When a problem requires multiple steps, store your intermediate answer rather than writing it down and re-entering it. This reduces transcription errors and speeds up your workflow.
4. Know when NOT to use the calculator. Some problems are faster to solve by inspection, estimation, or using the FE reference handbook formulas directly. Do not reach for the calculator on every single question. If you can eliminate answer choices quickly by order-of-magnitude reasoning, do that first.
5. Replace the battery before exam week. The TI-36X Pro uses a single CR2032 coin cell battery. Do not plan on opening the calculator during the exam; if you want redundancy, bring a second approved calculator and store it with your belongings under test-center rules.
6. Reset your calculator before the exam. Clear all stored data and reset your calculator to its default settings the morning of the exam. This ensures you start with a clean slate and avoids any confusion from leftover values in memory.

How Should You Practice with Your Calculator Before Exam Day?

This cannot be overstated: your calculator is a tool, and like any tool, you need to practice with it before you rely on it under pressure. Many examinees buy the TI-36X Pro a week before their exam and barely learn the basics. That approach leaves significant time savings on the table.

Here is what a solid calculator practice plan looks like:

• Start using your exam calculator at least 4 to 6 weeks before test day. Use it for all of your study problems so that it becomes second nature.
• Work through AC circuit problems using complex mode. Practice entering impedances in polar and rectangular form, computing parallel combinations of complex impedances, and converting results between forms.
• Solve 2x2 and 3x3 systems using the matrix function. Set up mesh analysis and nodal analysis problems and solve them entirely on the calculator.
• Practice the numeric solver on equations from the reference handbook. Pick formulas from the FE reference handbook, plug in known values, and solve for different unknowns to build familiarity.
• Time yourself. When doing practice exams, use your calculator under realistic time pressure. The goal is for calculator operations to feel effortless so your mental energy stays focused on the engineering concepts.

The difference between someone who has practiced with their calculator for weeks and someone who is learning it during the exam is measurable in time. At 110 questions in 5 hours and 20 minutes, the average pace is about 2.9 minutes per question. Saving even 15-30 seconds on repeated calculations gives you more time for flagged problems and reduces rushed arithmetic errors.

What Other Purchases Do You Need for Exam Day?

While your calculator is the most important tool, a few other purchases can help you prepare more effectively:

• NCEES FE Practice Exam ($50 from NCEES directly) — The only practice exam written by the same organization that writes the real test. Take it as a timed diagnostic 2 to 3 weeks before your exam date.
• NCEES FE Reference Handbook — Practice with the official digital handbook assigned to your exam date. Build search habits around section names, formula context, and units instead of relying on a paper-page memory.
• Backup approved calculator or spare CR2032 — Replace the battery before exam week and keep any backup with your stored belongings unless test-center staff permits otherwise.

What Is the Bottom Line?

The TI-36X Pro is the most capable calculator on the NCEES-approved list for most FE candidates. Its complex number support, matrix operations, numeric solver, statistics tools, and memory workflows map directly onto repeated problem types. Pick one model early, learn the button paths, and make calculator fluency part of practice instead of an exam-week side task.

TI-36X Pro Workflows and Worked Keystrokes

This section consolidates the former TI-36X Pro tutorial into the calculator guide so the approved-calculator comparison, function guide, and worked keystrokes live on one stronger page.

Quick answer: Master the TI-36X Pro calculator for your FE or PE exam with step-by-step keystroke tutorials, real exam-style problems, Guided Calculator Drills, and a function guide.

Source note: TI-36X Pro examples should be paired with current exam-day calculator policy. Verify approved models on the NCEES calculator policy before treating any calculator workflow as exam-ready.

The TI-36X Pro is the most popular NCEES-approved calculator for the FE and PE exams, and for good reason. It packs a numeric solver, polynomial solver, system of equations solver, matrix editor, and full statistics suite into a calculator you can check at its current Amazon price. These built-in features can save you minutes per problem on exam day — if you know how to use them.

This tutorial walks through the TI-36X Pro features that matter most for engineering exams, using actual exam-style practice problems you might encounter on the FE or PE. Each section shows the exact keystrokes so you can follow along with your calculator in hand. If you are still deciding which calculator to buy, check out our complete calculator buying guide for the full list of NCEES-approved models.

Before you start: Make sure your TI-36X Pro is in DEG mode (not RAD). Press mode and check that DEGREE is highlighted. This matters for every trig calculation on the exam.

Practice These Keystrokes in Guided Calculator Drills

Reading a calculator walkthrough is useful, but exam-day speed comes from pressing the buttons yourself. The FE Test Prep app now includes Guided Calculator Drills with TI-36X Pro shortcut practice, a built-in calculator beside the lesson, and a plain-English function guide for the calculator tools that save the most time.

• Guided drills for poly-solv, sys-solv, num-solv, complex numbers, BASE-N, statistics, unit conversions, and order-of-operations traps
• Discipline tracks so Civil, ECE, Mechanical, Chemical, Environmental, and PE Power students see the calculator functions most relevant to their exam
• Built-in calculator practice so you can follow each drill step by step without leaving the app

Open Guided Calculator Drills →

1. The Numeric Solver

The numeric solver is arguably the most powerful feature on the TI-36X Pro. It can solve any single-variable equation numerically, which means you can skip the algebraic rearrangement and let the calculator do the heavy lifting. On the exam, this is perfect for equations that are tedious to solve by hand or that involve transcendental functions.

Exam-Style Problem: Solve for x: 3x² − 12 = 0

By hand: 3x² = 12, so x² = 4, so x = ±2.

Using the numeric solver:

2nd sin (num-solv above the sin key) → Enter the equation: 3 x x² − 1 2
Press enter to confirm the equation
Set an initial guess (try x = 1) → press enter to solve
Result: x = 2

The numeric solver finds one root at a time. To find the negative root, re-enter the solver and use an initial guess of x = −1 to get x = −2. On the exam, the answer choices will tell you which root they are looking for.

When to use it: Any time you have an equation in one variable that is not trivially solvable — exponential equations, trig equations, or anything where you would spend more than 30 seconds rearranging by hand. On the FE exam, this alone can save 2–3 minutes per problem.

2. The Polynomial Solver

The polynomial solver handles quadratic and cubic equations by factoring the characteristic polynomial. You enter the degree and coefficients, and the calculator returns all roots — including complex roots. This is essential for differential equations, controls, and structural analysis problems where you need eigenvalues or characteristic roots.

Exam-Style Problem: Find the eigenvalues of the matrix A = [[4, 2], [1, 3]].

Setup: The characteristic equation is λ² − 7λ + 10 = 0 (from det(A − λI) = 0).

Using the polynomial solver:

2nd cos (poly-solv above the cos key)
Select degree: 2 (quadratic)
Enter coefficients: a₂ = 1, a₁ = (-) 7, a₀ = 1 0
Press enter to solve
Result: x₁ = 5, x₂ = 2

So λ = 5 and λ = 2. You can verify: the eigenvalues should sum to the trace (4 + 3 = 7) and multiply to the determinant (12 − 2 = 10). Both check out.

When to use it: Quadratic or cubic equations from characteristic equations, vibration problems (natural frequencies), control system poles, or any problem where you need roots of a polynomial. The polynomial solver is faster than the quadratic formula because you do not have to worry about sign errors in the discriminant.

Tip: The TI-36X Pro polynomial solver handles up to degree 3 (cubic). For quartic or higher, use the numeric solver instead with different initial guesses for each root.

3. The System of Equations Solver

Many FE and PE exam problems reduce to a system of 2 or 3 simultaneous linear equations — circuit analysis (KVL/KCL), statics (equilibrium), or material balances. The system solver handles 2×2 and 3×3 systems directly from the coefficient matrix.

Exam-Style Problem: Solve the system:
2x + 3y = 13
4x − y = 5

Using the system solver:

2nd tan (sys-solv above the tan key)
Select size: 2 (two equations, two unknowns)
Enter coefficients for equation 1: a₁ = 2, b₁ = 3, c₁ = 1 3
Enter coefficients for equation 2: a₂ = 4, b₂ = (-) 1, c₂ = 5
Press enter to solve
Result: x = 2, y = 3

Verify: 2(2) + 3(3) = 4 + 9 = 13 and 4(2) − 3 = 8 − 3 = 5. Both equations satisfied.

When to use it: Any problem that gives you simultaneous equations — mesh analysis in circuits, force equilibrium in statics, mass and energy balances in thermodynamics. The solver also handles 3×3 systems, which appear in three-mesh circuits and 3D statics problems.

4. The Matrix Editor

The matrix editor lets you enter, store, and operate on matrices directly. The most common exam use is computing determinants, but it also handles matrix multiplication and addition. For a 2×2 matrix, computing the determinant by hand is easy enough, but for 3×3 matrices the calculator eliminates arithmetic errors.

Exam-Style Problem: Given A = [[2, 1], [3, 4]], what is det(A)?

By hand: det(A) = (2)(4) − (1)(3) = 8 − 3 = 5.

Using the matrix editor:

2nd ln (matrix above the ln key) → select edit
Set dimensions: rows = 2, columns = 2
Enter values: [2, 1] then [3, 4]
Press 2nd quit to exit editor
2nd ln → select math → select det
2nd ln → select matrix [A] → ) enter
Result: 5

When to use it: Determinants, especially 3×3 matrices where cofactor expansion by hand is error-prone. Also useful for multiplying matrices in structural analysis stiffness problems or verifying inverse matrices.

5. Rectangular to Polar Conversion

Complex number conversions between rectangular (a + jb) and polar (r∠θ) form appear constantly on the FE exam — in circuit analysis (impedances, phasors), signal processing, and even basic math. The TI-36X Pro has dedicated conversion functions that eliminate the manual trigonometry.

Exam-Style Problem: Convert the complex number z = 3 + j4 to polar form.

By hand: |z| = √(9 + 16) = 5, θ = arctan(4/3) = 53.13°. So z = 5∠53.13°.

Using the R-to-P converter:

2nd R↔P → select R→Pr(
Enter: 3 , 4 ) enter
Result: r = 5 (magnitude)

2nd R↔P → select R→Pθ(
Enter: 3 , 4 ) enter
Result: θ = 53.13° (angle)

You need two separate calls: one for the magnitude (Pr) and one for the angle (Pθ). The reverse conversion (polar to rectangular) uses P→Rx and P→Ry.

When to use it: AC circuit analysis with phasors, impedance calculations, any problem involving complex numbers in polar form. On the FE Electrical exam, you might use this 10+ times. Make sure you know whether the problem expects degrees or radians for the angle — check your calculator mode.

6. Statistics and Distributions

The FE exam probability and statistics section includes problems on descriptive statistics (mean, standard deviation, regression) and probability distributions (normal, binomial). The TI-36X Pro can compute all of these from its data editor.

Exam-Style Problem: A sample of five voltage measurements yields: {10, 12, 14, 11, 13} V. The sample standard deviation is most nearly:

Using the statistics mode:

data → Clear any existing data if prompted
Enter values: L1 = 10, 12, 14, 11, 13 (press ↓ after each entry)
2nd data (stat-reg/distr above the data key) → select 1-Var Stats
Set Data = L1, FRQ = ONE → press enter to calculate
Scroll through results:
  Mean (x̄) = 12
  Sample std dev (S_x) = 1.58
  Population std dev (σ_x) = 1.41

Important: The exam almost always asks for the sample standard deviation (S_x, divides by n−1), not the population standard deviation (σ_x, divides by n). Read the problem carefully. If it says "sample" or gives you a sample of measurements, use S_x = 1.58.

The TI-36X Pro also has built-in normal distribution functions under 2nd data → Distributions:

• normalcdf(lower, upper, μ, σ) — area under the normal curve between two values
• invNorm(area, μ, σ) — find the z-value for a given percentile
• binompdf / binomcdf — binomial probabilities

These replace the standard normal tables provided in the reference handbook and are often faster than table lookups, especially for non-standard values.

7. Logarithms and Exponentials

Many exam problems involve logarithms, and it is critical to know which button to press. The TI-36X Pro has two logarithm buttons, and mixing them up is one of the most common calculator errors on the exam.

Know the difference:

• log = common log (base 10) — used for pH calculations, decibels, Richter scale
• ln = natural log (base e) — used for kinetics, decay, growth rates, time constants

Example: pH calculation. If [H+] = 0.001 M, then pH = −log(0.001):

(-) log 0 . 0 0 1 ) enter
Result: 3

Example: Half-life calculation. If a reaction has a half-life of 20 minutes and follows first-order kinetics, the rate constant k = ln(2)/20:

ln 2 ) ÷ 2 0 enter
Result: 0.03466 min−¹

If you need a logarithm with a different base (say log base 2), use the change-of-base formula: log₂(x) = ln(x) / ln(2). The TI-36X Pro also has a logBASE function under 2nd log that does this directly.

8. Engineering Notation and Scientific Notation

Engineering problems involve numbers with large or small magnitudes — resistances in megaohms, currents in milliamps, pressures in kilopascals. Entering these quickly using the EE key prevents digit-counting errors.

Entering 1.8 × 10−&sup5;:

1 . 8 EE (-) 5
Display shows: 1.8E−5

Common examples:

• 47 kΩ → 4 7 EE 3 (47E3)
• 2.2 μF → 2 . 2 EE (-) 6 (2.2E−6)
• 3.5 MPa → 3 . 5 EE 6 (3.5E6)

You can also toggle the display format between normal, scientific, and engineering notation by pressing mode and selecting your preference. Engineering notation displays exponents in multiples of 3 (matching metric prefixes like kilo, mega, micro), which many engineers find more readable.

9. Numeric Integration and Derivative

The TI-36X Pro has built-in numeric integration (2nd ∫) and numeric derivative (2nd d/dx) functions. These compute definite integrals and point derivatives numerically.

Example: Evaluate the definite integral of (4x³ + 6x²) from 0 to 1.

2nd ∫
Enter expression: 4 x ^ 3 + 6 x x²
Set lower bound: 0, upper bound: 1
Press enter to compute
Result: 3

Reality check: While these functions work, they are slow on the TI-36X Pro. A numeric integration can take 10–30 seconds to compute, and the exam clock does not stop while you wait. For most exam problems, applying the antiderivative by hand (power rule, substitution) and evaluating at the bounds is actually faster. Use the numeric integrator as a check when you have time, or as a last resort when you cannot find the antiderivative.

The numeric derivative is similarly useful as a check: if you computed f'(2) = 7 by hand, you can verify with 2nd d/dx to confirm.

10. Quick Tips for Exam Day

Beyond the specific features above, here are the calculator habits that separate well-prepared examinees from everyone else:

• Practice with the same calculator you will use on exam day. Do not practice on a phone app or different model and expect to be fluent with the TI-36X Pro under exam pressure. Muscle memory matters.
• Reset before the exam. Press 2nd reset enter to clear all memory and restore factory defaults. This ensures no leftover data or settings interfere with your calculations, and it satisfies the proctor if they ask you to clear your calculator.
• Stay in DEG mode. The vast majority of FE and PE exam problems use degrees. Only switch to RAD when a problem explicitly uses radians (rare outside of calculus-heavy problems). If you get a wildly wrong answer on a trig problem, the first thing to check is your angle mode.
• Use ans to chain calculations. After any computation, the result is stored in ans. You can use it in the next calculation by pressing ans or just starting with an operator (the calculator automatically inserts ans). This avoids rounding errors from re-entering intermediate results.
• Store intermediate results in memory variables. Press sto then a variable letter (x, y, z, t, a, b, c, or d) to save a value. Recall it later by pressing rcl and the variable letter. This is invaluable for multi-step problems where you compute an intermediate value (say, a Reynolds number) and need it in a later formula.
• Know your parentheses. The TI-36X Pro follows EOS order of operations, and division and multiplication at the same priority are evaluated left to right. If a formula means 1/(2π), type 1 ÷ ( 2 × π ). Typing 1 ÷ 2 × π gives π/2 instead.
• Know the blue-label shortcuts. Frequently used TI-36X Pro second functions include 2nd sin for num-solv, 2nd cos for poly-solv, 2nd tan for sys-solv, and 2nd ln for matrix. These save more time than hunting through menus.
• Bring fresh batteries. The TI-36X Pro uses a single CR2032 coin cell. Replace it a week before the exam so you know it will last the full 5+ hours. You cannot change batteries during the exam.

The one-week rule: Starting one week before your exam, do every practice problem with your TI-36X Pro in hand. By exam day, every keystroke should be automatic. If you have to think about where a function is, you are spending time you should be spending on the problem.

More study resources:

🔢 Calculator Buying Guide • 📐 Handbook Navigation Guide • ✅ Exam Day Checklist • 📅 Study Schedules • 📕 Best Prep Books

Frequently Asked Questions

Is the TI-36X Pro allowed on the FE exam?

Yes. The TI-36X Pro is on the official NCEES list of approved calculators for all FE exam disciplines. You do not need to request permission or get any special approval — just bring it to the testing center on exam day. See our calculator guide for the full approved list.

Can I use the TI-36X Pro on the PE exam?

Yes. The NCEES calculator policy applies across FE and PE exams. The TI-36X Pro is in the approved TI-36X family for 2026, but verify the current NCEES exams page before your exam date.

Should I buy the TI-36X Pro or a Casio fx-115?

Both are NCEES-approved and fully capable. The TI-36X Pro has more built-in solvers (numeric solver, polynomial solver, system of equations solver), which can save significant time on computational problems. The Casio fx-115 has a slightly different interface that some people prefer. Choose whichever you are more comfortable with, but make sure to practice extensively with your chosen calculator before exam day. See our calculator buying guide for a detailed comparison.

What mode should my calculator be in for the exam?

DEG (degrees) mode for almost everything. The vast majority of FE and PE exam problems use degrees for angles. Only switch to RAD mode when a problem explicitly states radians or involves calculus expressions where radians are assumed. Always double-check your mode before starting a trig calculation.