Eighty4

A TI-84 Plus CE replica for iPhone, built in SwiftUI. No ROM, no emulation: the body, keypad, 320×240 display, home-screen math engine, menus, graphing, and a couple of built-in games are all reimplemented from scratch so the app can ship on its own.

Eighty4 is an independent project and is not affiliated with or endorsed by Texas Instruments. "TI-84 Plus CE" is a trademark of Texas Instruments.

Features

Hardware look

• Body drawn at real proportions (86.9 × 190.5 mm design grid) with the glossy bezel, side USB-C port and charge LED.
• Full 10×5 keypad with the blue 2nd and green alpha overlays on every key, white digit keys, charcoal function keys, and a round D-pad with wedge-shaped hit regions.
• Six official shell colorways: Black, Radical Red, Rose Gold, Galaxy Gray, Trinomial Teal, Bionic Blue. Tap the palette button above the calculator, or long-press the wordmark.
• App homepage. The app opens on its own home screen: pick Eighty4+ CE or Eighty4 Evo, with Eighty4 30Xa, Eighty4 30XS, Eighty4 36X Pro, Eighty4+ SE, Eighty4+ and Eighty4 Nspire (the TI-30Xa, TI-30XS MultiView, TI-36X Pro, TI-84 Plus SE, TI-84 Plus and TI-Nspire CX) listed as coming soon. The grid button above the calculator goes back to it.
• Two calculators in one app. The palette sheet switches between Eighty4+ CE (TI-84 Plus CE) and Eighty4 Evo (TI-84 Evo). The Evo has its own body (light one-piece face, big square keys with 2nd/alpha printed on them, White / Pink / Mint / Raspberry / Silver / Teal / Lavender shells), its keypad copied from the real unit (plot/tblset/format/calc/table with f1–f5, =≤≠> on math, n/d fraction key, x^□ with ⁿ√ on 2nd, ÷ × − + one row up, matrix on 2nd+vars, distr on alpha+stat, ↰clear Undo, recall, ◂▸ toggle key, on = home, black digit keys, a four-arrow pad whose 2nd+◀/▶ jump to the ends of a line), the icon home screen (Calculator, Y= Editor, List Editor, Mode, Numeric Solver, Poly Root Finder, System Solver, Finance, Transformation, Inequality, Lines & Conics, Python, TI-Basic, Help), green answers with a blue insertion cursor that never overwrites, a dot for multiplication, a white header naming the app you are in, ◂▸ fraction/decimal toggling, 2nd+clear Undo, the log key as log-of-any-base, alpha+f1–f4 shortcut menus, ◂▸ syntax help in menus, MODE with GRADIAN / DIAGNOSTICS / LANGUAGE, STAT with EDIT · CALC · INTERVALS · TESTS and PropReg / RecipReg / eBASEReg, DISTR grouped by distribution, ZDecimal as the default window, Points-of-Interest tracing that snaps to zeros, extrema, intercepts and intersections, a Help app and a small Python shell.
• Haptic key presses.

Home screen

• 26-column × 10-line display with the status bar, battery, blinking cursor, 2nd (↑) and alpha (A) indicators, INS underline cursor.
• TI-style results: 10 significant digits, .5 without a leading zero, ⁻ negation glyph, ᴇ exponent notation, NORMAL / SCI / ENG and FLOAT / FIX 0–9 from the MODE screen.
• ↑ / ↓ scroll back through previous entries and answers like the CE: ENTER pastes the highlighted one at the cursor, DEL or CLEAR removes that entry/answer pair (Ans follows what is left on screen). 2nd+ENTRY recalls the last entry, 2nd+RCL pastes a variable's value. CLEAR on an empty line wipes the screen and resets Ans to 0.
• DEL, ◀/▶ and overwrite work on whole tokens: sin( or √( goes in one press, as on the real keypad.
• MODE MATHPRINT / CLASSIC: in MathPrint the MATH FRAC menu inserts stacked n/d and Un/d templates (dotted boxes for empty slots, ◀/▶ move between numerator and denominator, DEL removes the whole template), MATH piecewise( asks for 1–5 pieces and draws the brace, and fraction answers come back stacked. MODE ANSWERS AUTO / DEC / FRAC decides whether 1/2+1/4 shows 3/4 or .75. CLASSIC keeps everything on one line.
• Hardware keyboard (iPad keyboard, Mac, simulator): digits and operators type directly, letters go through alpha, sin( / randint( typed as words become the function tokens, ! % < > = ≠ ≤ ≥ ° ' _ π √ { } [ ] insert their tokens, Return = ENTER, Esc = CLEAR, Backspace/Delete = DEL, arrows = D-pad, F1–F5 = y= window zoom trace graph.
• Errors show the real ERR: screen with 1:Quit / 2:Goto.

Math engine

• Reals, fractions (▶Frac), lists ({1,2,3}, L₁–L₆), and matrices ([[1,2][3,4]], [A]–[J]) with TI precedence, implicit multiplication, and → store into A–Z, θ, lists, matrices, and Y-vars.
• MATH: ▶Frac ▶Dec ³ ³√( ˣ√ fMin( fMax( nDeriv( fnInt( Σ( logBASE( and the numeric Solver — type an expression (X²−4) or a whole equation (2X+3=11), set a guess and the search bounds, alpha+ENTER solves (ENTER on the Evo), NUM (incl. toString( eval(), PROB (rand nPr nCr ! randInt( randNorm( randBin( randIntNoRep(), FRAC with Un/d mixed numbers (3_1/2), %.
• Complex lists: {1+i,2}, element-wise + − × ÷ ^ ², conj( real( imag( abs( angle( sum( prod( mean( dim( cumSum( augment(, stored in L₁–L₆.
• Complex matrices: [[1,i][2,3]], [A]×i, + − × ² ^n ⁻¹ ᵀ det( conj( real( imag( abs( dim( augment( cumSum( ref( rref( rowSwap( row+( *row( *row+( Fill( Matr▶list( List▶matr(, stored in [A]–[J] and typed straight into the matrix editor (3+i in a cell). MATH piecewise(expr,cond,…) evaluates lazily and graphs.
• Complex numbers: i (2nd+.) in any mode, + − × ÷ ^ ² ⁻¹ √( ln( log( e^( abs( conj( real( imag( angle( ▶Rect ▶Polar, complex values in A–Z/θ, and the MODE REAL / a+bi / re^θi setting: √(⁻4) and (⁻8)^(1/3) give 2i and 1+1.732050808i in a+bi mode, ERR:NONREAL ANS in REAL mode; re^θi shows 2e^(1.570796327i).
• TEST and LOGIC operators, ANGLE (° ' ʳ ▶DMS R▶Pr( R▶Pθ( P▶Rx( P▶Ry(), radian/degree modes.
• LIST OPS and MATH (SortA( SortD( dim( Fill( seq( cumSum( ΔList( augment( min( max( mean( median( sum( prod( stdDev( variance().
• MATRIX MATH (det( ᵀ dim( Fill( identity( randM( augment( Matr▶list( List▶matr( cumSum( ref( rref( rowSwap( row+( *row( *row+(), inverse, powers, and a spreadsheet-style matrix editor.
• DISTR: normalpdf normalcdf invNorm invT tpdf tcdf χ²pdf χ²cdf Fpdf Fcdf binompdf binomcdf invBinom poissonpdf poissoncdf geometpdf geometcdf, and DRAW ShadeNorm( Shade_t( Shadeχ²( ShadeF( shade the density on the graph screen.
• STAT: list editor for L₁–L₆, CALC with 1-Var Stats, 2-Var Stats, Med-Med, LinReg (both forms), QuadReg, CubicReg, QuartReg, LnReg, ExpReg, PwrReg, Logistic, SinReg. Results land in the VARS Statistics variables and RegEQ.
• STAT TESTS: all 17 editors (Z-Test, T-Test, 2-Samp Z/T, 1-Prop/2-Prop Z, the Z/T/prop intervals, χ²-Test, χ²GOF-Test, 2-SampFTest, LinRegTTest, LinRegTInt) with Data/Stats input, Calculate or Draw (shaded p-value), plus ANOVA(. Results go to VARS Statistics TEST.
• Strings: "…"→Str1, concatenation with +, length( sub( inString( expr(.
• Commands: ClrHome ClrDraw ClrAllLists ClrList PlotsOn/Off Degree Radian Float Fix Normal Sci Eng Func Param Polar Seq FnOn FnOff AxesOn/Off Grid… Coord… Label… Expr… ZStandard … ZFrac1/2 StorePic RecallPic StoreGDB RecallGDB BackgroundOn/Off, and the DRAW commands Line( Circle( Tangent( Shade( DrawF DrawInv Pt-On( Pt-Off( Pt-Change( Pxl-On( Pxl-Off( Pxl-Change( pxl-Test( Text( Horizontal Vertical. Pen draws free-hand on the graph.

Graphing

• All four MODE graph types: FUNCTION (Y₁–Y₀), PARAM (X₁T/Y₁T…), POLAR (r₁–r₆) and SEQ (u, v, w with nMin and u(nMin), recursive definitions like u(n−1)+u(n−2)). The Y= and WINDOW editors change with the mode (Tmin/Tmax/Tstep, θmin…, nMin/nMax/PlotStart/PlotStep).
• Y= editor with function on/off (← onto the =), WINDOW editor, FORMAT (grid, axes, labels, coordinates, expression), ZOOM (ZBox, Zoom In/Out, ZDecimal, ZSquare, ZStandard, ZTrig, ZInteger, ZoomStat, ZoomFit, ZQuadrant1, ZFrac1/2 1/3 1/4, ZPrevious, ZoomSto/Rcl, SetFactors).
• GRAPH plots every enabled function in its TI color, plus STAT PLOT scatter / xyLine plots, DRAW objects, pictures and BackgroundOn colors.
• TRACE with ←/→ (steps of Tstep/θstep/PlotStep in the other modes), ↑/↓ to switch functions, or type a value.
• CALC: value, zero, minimum, maximum, intersect, dy/dx, ∫f(x)dx with the real bound / guess prompts.
• TABLE with TBLSET (TblStart, ΔTbl), scrolling in both directions, columns per graph mode.
• VARS: Window (X/Y, T/θ, U/V/W), Zoom, GDB, Picture, Statistics (incl. TEST), Table, String; Y-VARS Function / Parametric / Polar / Sequence / On-Off.

Everything else on the keypad

• MODE, FORMAT, TBLSET, STAT PLOT editors that look and navigate like the originals.
• APPS: GeoDash (one level, ↑/enter to jump), Tetris (←→ move, ↑ rotate, ↓ soft drop, enter hard drop), Finance (a working TVM Solver; alpha+ENTER solves the highlighted row), CabriJr (points, segments, lines, circles, triangles, distance), CelSheet (spreadsheet with A1-style formulas and ranges), Conics (graph + center/vertices/foci/eccentricity), Inequalz (Y= and X= relations shaded on the graph), PlySmlt2 (polynomial roots incl. complex, simultaneous equations), Prob Sim (coins, dice, marbles, spinner, cards, random numbers), SciTools (sig-fig calculator, unit converter, data wizard, vector calculator), Transfrm (Y₁ with live A B C D sliders) and Vernier EasyData (sensor front-end; reports no sensor without hardware).
• PRGM: EXEC runs the two games and your TI-BASIC programs, EDIT opens the program editor (PRGM key inside it shows the CTL / I/O / EXEC menus), NEW creates one and asks "Program Lock?": a locked program runs from EXEC but shows [LOCKED] in EDIT and must be unlocked (2:Unlock) before it opens. The interpreter handles Disp Input Prompt Output( ClrHome Pause If/Then/Else For( While Repeat End Lbl Goto Menu( IS>( DS<( Return Stop DelVar DispGraph DispTable getKey prgmNAME and every expression/command the home screen accepts. Errors offer 2:Goto into the editor.
• MEM: About, Mem Management/Delete by category (DEL deletes, ENTER archives), Clear Entries, Archive/UnArchive, Reset (RAM, defaults, ARCHIVE vars/apps/both with the 1:No 2:Reset screens), Group/Ungroup, Garbage Collect. LINK shows the send/receive flow. CATALOG lists every token, alphabetically, with letter jumps.
• 2nd+OFF turns the screen off; ON turns it back on.

Building

Requirements: Xcode 26, xcodegen (brew install xcodegen).

xcodegen generate          # creates Eighty4.xcodeproj from project.yml (the xcodeproj is gitignored)
open Eighty4.xcodeproj     # pick an iPhone simulator and run

From the command line:

xcodebuild -project Eighty4.xcodeproj -scheme Eighty4 \
  -destination 'platform=iOS Simulator,name=iPhone 17 Pro Max' build
xcodebuild -project Eighty4.xcodeproj -scheme Eighty4 \
  -destination 'platform=iOS Simulator,name=iPhone 17 Pro Max' test

Demo launch arguments

Useful for screenshots. -demo wipes saved memory first.

Argument	What it shows
-demo home	Home screen with worked history
-demo math, mode, window, catalog	Menus and editors
-demo yeq, graph, trace, calc, table	Graphing flow for Y₁=X²−4, Y₂=2X+1
-demo matrix, matrixcalc, stat, statcalc	Matrix and list editors, LinReg
-demo geodash, tetris, tvm	Apps
-demo solver, param, polar, seq, seqyeq, zbox, shade	Solver, graph modes, ZBox, ShadeNorm
-demo ztest, ztestedit, ztestdraw	STAT TESTS editor, results and DRAW
-demo prgm, prgmedit, mem	Program run / editor, MEM management
-demo complex, inequalz, prgmlock	Complex results and a complex list in a+bi mode, Inequalz Y= and X= shading, the "Program Lock?" screen
-demo plysmlt, conics, probsim, celsheet	The new apps
-shell radicalRed	Force a shell colorway (any ShellColor raw value)

Example:

xcrun simctl launch booted com.sachi.eighty4 -demo graph -shell bionicBlue

Project layout

project.yml            xcodegen spec (targets, version, Info.plist keys)
Eighty4/
  Eighty4App.swift     entry point + demo scripts
  Models/              KeySpec, Keymap (all 50 keys with 2nd/alpha labels), Shell colors
  Engine/              Tokenizer → Parser → Functions / Stats / StatTests / Sequences / Solver / Programs (TI-BASIC), VariableStore
  State/               Screens, Menus, Editors, Graphing, CalculatorState, KeyHandler
  Apps/                Game protocol + AppKit helpers, GeoDash, Tetris, CabriJr, CelSheet, Conics, Inequalz, PlySmlt2, ProbSim, SciTools, Transfrm, Vernier
  Views/               Layout (0.1 mm design units), body, keypad, LCD, graph renderer and screen views
Eighty4Tests/          engine + key-flow unit tests
assets/logo.png        source logo (app icon + wordmark badge)

Version history

• 1.1.0 — An app homepage that picks the calculator (and lists the models still to come), plus Eighty4 Evo: a second model (TI-84 Evo) with its own body and keypad taken from the real unit — plot/tblset/format/calc/table with f1–f5, =≤≠> on math, the n/d fraction key, x^□ with ⁿ√, matrix on 2nd+vars and distr on alpha+stat, ↰clear Undo, recall, the ◂▸ toggle key, on+home, black digit keys and a four-arrow pad whose 2nd+◀/▶ jump to the ends of a line. Also the Evo's icon home screen and app-name header, green answers and bar cursor, GRADIAN, the four-tab STAT menu with PropReg/RecipReg/eBASEReg, grouped DISTR, ZDecimal default, Points-of-Interest trace, Help and Python. Fixed the equation solver: an equation written with = used to evaluate as a true/false test so the solver just returned the guess, and opening any menu from the solver threw the equation away. The bound row is editable now, roots are verified before they are reported, and the Evo solves with ENTER.
• 1.0.1 — The rest of MathPrint on the home screen: ^ / eˣ / 10ˣ type a raised exponent slot, √( and ˣ√ / ³√( draw a radical with a vinculum, logBASE( a subscript base, abs( its bars, and Σ(, nDeriv(, fnInt( the Σ, d/dx and ∫ templates with stacked bounds; ▶ leaves a slot, DEL removes a whole template, CLASSIC mode still types the flat tokens.
• 1.0.0 — MathPrint: MODE MATHPRINT/CLASSIC with stacked n/d and Un/d fraction templates, piecewise( with its brace (1–5 pieces), stacked fraction answers and MODE ANSWERS AUTO/DEC/FRAC; complex matrices everywhere real ones work, including the matrix editor; ▶Frac/▶Dec/… convert the whole entry (1÷4▶Frac is 1/4, not 1÷(4▶Frac)); fixed a crash in identity(.
• 0.4.0 — Complex arithmetic with the REAL / a+bi / re^θi modes and ERR:NONREAL ANS, complex variables and complex lists, Program Lock on PRGM NEW, toString( eval( invBinom( %; CE-style ↑/↓ scroll-back with ENTER paste and DEL/CLEAR pair removal; token-wise DEL/cursor/overwrite; hardware keyboard input; Inequalz X= relations.
• 0.3.0 — Nothing says "not available" any more: MATH Solver, Un/d, DISTR DRAW shading, Fill/Matr▶list/List▶matr/row ops, GDB/Pic/String variables, PARAM/POLAR/SEQ graphing with matching Y=/WINDOW/TABLE, all STAT TESTS + ANOVA + Logistic/SinReg, DRAW Tangent/Shade/DrawInv/Pen/pixel ops/StorePic/BackgroundOn, ZBox/ZFrac/SetFactors, MEM archive/groups/garbage collect/reset archive with confirm screens, a TI-BASIC program editor + interpreter, and nine more apps (CabriJr, CelSheet, Conics, Inequalz, PlySmlt2, Prob Sim, SciTools, Transfrm, Vernier).
• 0.2.0 — Every 2nd function and menu key works: menus, MODE/FORMAT/WINDOW/TBLSET/STAT PLOT editors, Y= and graphing with TRACE / CALC / TABLE / ZOOM, lists, matrices and their editors, stats and regressions, distributions, TVM solver, CATALOG, MEM, LINK, GeoDash and Tetris apps, shell color button, LCD fills the bezel, ENTER works under 2nd/alpha, history recall on ↑/↓.
• 0.1.0 — Faithful body and keypad, home-screen arithmetic, shell colorways.