Calculator ft+

Everything lives on one screen. Tap a label below to highlight where it sits.

Main display — the value with its unit. Tap to arm save mode; press-hold to edit it on the entry keyboard (chapter 13). Expression row — the whole calculation written out. FT | RPL switch — flips the whole chassis between the construction calculator and the RPL machine (chapter 23). Units panel — the value converted to all nine length units, live. Feet–inch–fraction readout — ft + in + n/64ths. Press-hold to edit it directly as "5 ft 3 1/4 in". Store slots — 18 named memories. Values keep their units and survive restarts. History stack — every entry and result with its unit. It grows without limit; tap any row to recall. Help feed — narrates every action and explains keys. Scroll it, or tap for the full session view. Settings & About — the gear opens preferences; the ⓘ opens the About page. Mic & keyboard — speak a request, or type one over the help window. Function pages — 6 colour-coded pages of operations. Swipe or tap the dots. Prime keys — X², √, % and a big enter, always visible. Press-hold a prime to swap in any key you like (chapter 17). reset · undo · ans · x↔y — the right-hand prime column. Operators — − + × ÷ down the left edge. Keypad — digits, decimal point and ±. Unit column — three pages: lengths; time, mass, force & speeds; surveying units. Press-hold a key to drag it into your own order. Fraction keys — three pages from quarters to 64ths, plus X/32 and X/64.

Calculator ft is a Reverse Polish Notation calculator: you push values onto a stack with enter, then apply an operation. There is no equals key — an operator computes immediately using the values already on the stack.

ans and x↔y sit in the right prime column; the rest of the stack keys live on the last function page:

Digits, . and ± work as expected. Three keys deserve a note:

Display precision

Results show 8 decimal places. Outside the everyday range the display switches to scientific notation automatically, so a tiny result is never mistaken for zero:

The nine-unit panel adapts its precision to the size of each number — every row gets a ~12-character budget:

Tap a gold unit key after a number and it becomes a length: the panel converts it to all nine units at once, and the feet–inch–fraction readout decomposes it the way a tape measure reads.

Feet–inch–fraction entry

Build a tape-measure value left to right: feet, then inches, then a fraction key.

Illustrated · 2 ft 3⅜ in

1Type 2 2Tap ft — feet are set, inches armed 3Type 3 4Tap in — inches added, fraction armed 5Tap 3/8 6Reads 2.28125000 ft — the panel shows all conversions

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Thirty-seconds & the fraction readout

X/32 turns the whole number on screen into 32nds of an inch: 5X/32→0.15625 in (= 5/32″). Going the other way, any length's inch remainder is snapped to the nearest 64th for the readout:

Mix units freely in one calculation. The rule is always the same:

Illustrated · 5.5 m + 6.5 ft

1Type 5 . 5 2Tap m — panel converts instantly 3enter pushes 5.5 m onto the stack 4Type 6 . 5 5Tap ft 6Press + 77.48120000 m — 6.5 ft became 1.9812 m, and the result keeps the first unit

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Chaining keeps units. Continue with 2× and you get 14.9624 m. Results re-enter the stack as full unit values, so a whole cutting-list calculation stays in your working unit from start to finish.

Lengths carry a dimension — a power of length. Multiplying lengths raises it, dividing lowers it, and the engine tracks it exactly:

Geometry keys produce properly-dimensioned results: πX² (circle area) and XY/2 (triangle area) give unit², π2X (circumference), 2(X+Y) (perimeter) and √(X²+Y²) (diagonal) give lengths. The m²⇾ft² / ft²⇾m² keys convert real areas in either direction.

Beyond lengths, every quantity carries an SI dimension vector (L, T, M) — exponents of length, time and mass. Multiplication adds the vectors, division subtracts them, and addition requires them to match:

Illustrated · F = m·g

1Scroll the unit column to its second page and type 1 0 2Tap kg — it is now a mass 3enter pushes 10 kg 4Swipe the function strip to page 3 — π & constants 5Tap g — standard gravity, 9.80665 m/s² 6Press × 798.06650000 N — mass × acceleration derived force

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Composite units generate themselves. An area divided by a time displays as m³/s-style composites when no named unit exists for the dimension vector. The constants g and c, and results from the kg⇾lb and mph⇾km/h converters, all participate in the algebra.

The DEG/RAD toggle on the last function page (or in Settings) sets the angle mode for all six trig functions and their inverses. Degrees is the default — the key shows the active mode, and the choice persists across restarts.

Roof pitch & grade

Two purpose-built cyan construction keys on page 5 take rise then run — in any mix of length units:

Eighteen store slots hold values with their units, and everything persists across app restarts. To save: tap the main display to arm save mode (slots turn white), then tap a slot. To recall: just tap a filled slot.

Illustrated · save & recall

1With 7.4812 m on screen, tap the display 2Save mode: slots turn white — tap one 3The slot reads 7.48120000 m. Press reset 4Tap the slot again to recall 5got: 7.4812 m — the unit came back too; ×2 gives 14.9624 m

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The history stack logs every entry and result with its unit — tap any row to bring it back, and note the display tap that arms save mode fires on release, so it never fights the press-hold editor. The stack grows without limit: when the visible grid fills, older values move into extra rows above it instead of being lost, and the whole column stays scrolled to the newest entries. ans (right prime column) recalls the newest entry without leaving the pages. Slots, the full history and the angle mode are all restored when the app relaunches.

Swipe the function strip or tap a page dot. Keys are colour-coded by role:

The prime columns flank every page: X² √ % and enter on the left (the top three are your slots — hold one to swap in any key, chapter 17); reset undo ans x↔y on the right. In the tables, x is the last-entered value and y the one before it.

Page 1 · Powers & roots

Key	Formula	Example
X² / X³	x², x³ — dimension-aware: (2 m)² = 4 m²	12 → 144
√ / ²√X	√x — halves even dimensions: √(9 m²) = 3 m	9 → 3
³√X	x^(1/3) — ³√(8 m³) = 2 m	27 → 3
X⁻¹	1/x	5 → 0.2
%	x / 100	50 → 0.5
Xʸ / Yˣ	y^x and x^y	3 enter 4 → 81 / 64
ʸ√X / ˣ√Y	y^(1/x) and x^(1/y)	8 enter 3 → 2
√(X²+Y²)	hypot(y, x) — the diagonal; a length if operands are lengths	3 m enter 4 m → 5 m
if X=100 Y=?	100·x / y — x as a percentage of y	50 enter 25 → 50 %

Page 2 · Trigonometry

sin, cos, tan, their inverses, and the hyperbolic family with inverses — twelve periwinkle keys. The circular six honour the DEG/RAD mode (chapter 08); inverse results are labelled with the active angle unit. Hyperbolic arguments are pure numbers.

Page 3 · π & constants

Key	Formula	Example
π/X / X/π	π/x and x/π	2 → 1.5708
πX²	π·x² — circle area from radius, dimension-aware	2 m → 12.5664 m²
π2X	2π·x — circumference from radius	2 m → 12.5664 m
XY/2	y·x/2 — triangle area; length×length → area	3 m enter 4 m → 6 m²
2(X+Y)	2(y+x) — rectangle perimeter	3 m enter 4 m → 14 m
π e φ γ g c	Constants — chapter 11; g and c carry real units	g → 9.80665 m/s²

Page 4 · Conversions

All twelve green one-shot converters on a single page: m²⇾ft² ft²⇾m² deg⇾rad rad⇾deg ℃⇾℉ ℉⇾℃ kg⇾lb lb⇾kg mph⇾km/h km/h⇾mph L⇾galᵁˢ galᵁˢ⇾L. Results are real tagged quantities — a converted mass or speed keeps participating in the dimensional algebra.

Page 5 · Exponentials, logs & construction

Key	Formula	Example
eˣ 2ˣ 10ˣ	exponentials of the displayed value	10ˣ: 3 → 1000
ln log₂ log₁₀	natural, binary and decimal logs	log₁₀ 1000 → 3
x!	factorial	5 → 120
mod	y mod x — unit-aware remainder	10 m enter 3 m → 1 m
pitch°	atan(rise/run) in degrees	6 enter 12 → 26.5651 deg
slope%	100·rise/run	6 enter 12 → 50 %
abs / round	|x| and round(x)	−2.5 → 2.5 / 3

Page 6 · Stack, combinatorics & statistics

Key	Formula	Example
DEG/RAD	angle-mode toggle — shows the active mode
EE	scientific-notation entry; twice for a negative exponent	1 EE EE 9 → 1e-9
drop dup rand	stack utilities — chapter 02
floor / ceil	⌊x⌋ and ⌈x⌉	2.3 → 2 / 3
nCr / nPr	combinations and permutations of y things taken x at a time	5 enter 2 → 10 / 20
logY	log of y in base x	8 enter 2 → 3
avg	(y + x)/2 — unit-aware average	2 m enter 4 m → 3 m
Δ%	100·(x − y)/y — percent change from y to x	50 enter 60 → 20 %

g and c are true quantities: they keep their units through arithmetic (g2×→19.6133 m/s²) and combine dimensionally (mass × g = force in newtons).

Length units (metres per unit)

Areas and volumes convert by the factor raised to the dimension: k^p — 1 m² = 10.76391 ft² because (1/0.3048)² = 10.76391.

Quantity units (SI factor · dimension vector L,T,M)

Press and hold the main value (or the feet–inch readout) and it becomes an editable field: place the cursor, select, erase and retype like text. A dark scrim isolates the edit, and a purpose-built construction keyboard comes up — number pad and Go bar on the left, every unit key in gold and every constant in orange on the right, and three rows of tape-measure fractions across the top.

Illustrated · edit to 5 ft 3¼ in

1With 5 on screen, press and hold the value 2The editor opens. Tap ft 3 ␣ 1/4 in 3Tap Go — or anywhere on the scrim — to commit 45.27083333 ft — the panel and the arch readout update instantly

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Constants carry units here too. The orange g key inserts 9.80665 m/s² and c inserts 299792458 m/s — commit one and the value enters the dimensional algebra as a real acceleration or speed. The E key types scientific-notation exponents (1.5E6), ± flips the sign, and / with the space key builds any custom fraction.

The two keys beside the help feed — ⌨ and 🎤 — both open the same compose surface, laid out down the screen: the help box takes what you said or typed, a reading panel below it shows what the calculator made of it and what that computes to, the suggestion strip rides above the keys, and the keyboard rises from the bottom exactly the way the press-hold value editor's does — same black ground, same keys. Nothing you say or type reaches the calculator until you commit it there, which is the point: dictation mishears, thumbs mistype, and you should see the interpretation before it becomes an entry.

The panel has two lines. The top one is what arrived — the transcript as the recogniser heard it, or exactly what you typed — and it is editable, so when one word comes out wrong you fix that word instead of saying the sentence again. Below it, READS AS shows what the calculator made of it, in the syntax of the mode you are in, with the result previewed underneath. The preview is computed for real but thrown away; only commit touches the stack.

A coloured dot reports how sure it is. Green means every word matched cleanly. Amber means something was corrected to get there, and the correction is named underneath — “meaters → meters”. Orange means part of the phrase was not understood and was set aside; the words it ignored are listed. Committing an amber or orange reading is perfectly reasonable once you have looked at it, which is exactly what the panel is for.

What it understands. Numbers as words or digits, decimals spoken as “point”, and tape fractions — “three and a quarter”, “and a half”. Feet-and-inches the way the trade says it: “five foot three” is 5 ft 3 in, not five plus three. Every unit the calculator knows, in singular, plural and abbreviation. The operators in words — plus, minus, times, over, divided by, per, to the power of, squared, cubed, square root of. Filler is discarded without complaint, so “ok so what is the total of three feet and two inches” is understood. And the names of your stored programs: “two sph” runs SPH on 2.

Partial results are kept. If the phrase runs out or turns to nonsense, whatever was understood still commits rather than being thrown away. “five feet plus” pushes 5 ft and leaves the + waiting on the command line, just as keying it would. “twelve times the whatsit” pushes 12 and tells you it ignored the rest.

The suggestion strip offers the word you are reaching for, drawn from the calculator's own vocabulary — units, operators, functions and every stored program name. It completes the word you are part-way through rather than appending to it, so tapping inches after typing “in” gives “inches”, not “in inches”. What it offers follows what you have already written: the words that open a calculation when the line is empty, and units and operators straight after a number.

Keys, clear and commit. The panel carries its own keyboard in the same dark style, so no grey system keyboard appears underneath and the whole thing reads as one object. Three planes, the way a phone does it: letters with ⇧ (tap once for one capital, twice to lock), 123 for digits and punctuation, and #+~ for the symbols a calculator actually wants — × ÷ √ π ² ³ ° and the ' and " that mean feet and inches. Space and erase are the widest keys. clear sits to the left of commit and empties the line without closing the panel.

The mic and keyboard keys are the calculator's own — the two that always flank the help box, microphone above and keyboard below. The keyboard key opens the surface and closes it again; the microphone key starts and stops listening and turns red while it does. Dictating and typing are the same surface, not two of them: the keys stay there while you speak, so a misheard word is one tap away from being fixed.

All of it runs on the device. Dictation uses the offline recogniser only — if a language has no offline model installed the panel says so rather than sending your audio anywhere. The recogniser is told the calculator's vocabulary in advance, which is why it hears “ft”, “yd” and “PENDUL” rather than guessing at them. No part of this feature makes a network connection, and no model is bundled: the understanding is a grammar over the calculator's own unit and command tables.

The gear opens Settings: displayed decimals (0–8), key sounds, haptics, the DEG/RAD angle unit, the guide & examples language (EN/ES), the RPL workspace, the Examples & modules library (searchable, with mode filters), this guide, the session view and the About page. The ⓘ key jumps straight to About, with Share Calculator ft and a link to macdevstudio.com/calculator. Both pages close with a tap on the background.

Your three prime slots

The three keys above enter are placement slots, preloaded with X² √ %. Press-hold one and it lights up orange; then tap any key on any function page — swipe pages freely while choosing — and that operation moves in, colour, formula pieces and all. Hold the slot again to cancel. Your choices persist across restarts, and the original keys always remain on their pages.

Illustrated · put sin in a prime slot

1Press-hold the X² prime slot 2It lights up orange — swipe to the trig page 3Tap sin 4sin is now a prime key — the feed confirms, and it sticks after a restart

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Reorder the unit column

Press-hold any key in the vertical unit column and drag it up or down — the other keys resettle around it. Repeat with as many keys as you like: put your everyday units at the top and the surveying page wherever suits the job. Tap Done to save; the order is restored every launch.

Settings → RPL mode opens a second calculator: a from-scratch implementation of the RPL language (via the open-source newRPL engine) with an infinite object stack, 32-digit arbitrary-precision reals, and every value a typed object — reals, integers, strings, lists, vectors, unit objects, programs « » and algebraics 'X^2+1'. ‹ Calc returns to the construction calculator; everything you build here is saved and restored across launches.

Menus & soft keys

The tab row selects a menu — VAR (your variables), MTH, TRIG, STK, LST, UNIT, PRG — and NXT pages through it. The six gold soft keys behave like a real HP: on an empty command line a command executes immediately; with text pending it types itself into the line. Structural tokens («, IF, STO, units…) always insert.

Objects on the stack

Tap a row to copy its contents into the command line. UNDO restores the previous stack (ten levels deep). Errors from the engine appear in a banner and leave your command line untouched for correction.

Programs are objects: anything between « and » is code you can store, pass around and run. Name one with STO and it appears in the VAR menu as a soft key — tap to run it.

Illustrated · store a program

1Type « 2 × » — operators become text inside a program 2ENTER — the program is an object on the stack 3Type 'DBL' in α mode 4STO (PRG menu) stores it 5DBL is now a VAR soft key: 7 ENTER DBL→14

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The full RPL control set is on the PRG menu: IF THEN ELSE END, FOR NEXT, START STEP, DO UNTIL, WHILE REPEAT, plus RCL and PURGE, and directories via CRDIR / UPDIR / HOME on the VAR menu's last page. The whole RPL memory — stack, variables, directories — is saved automatically and restored on the next launch.