The tape: a calculation you can go back and fix
Every line you enter stays on screen with its result beside it, and every line is still editable. Go back to line 2, change 120000 to 135000, and each line below it is recalculated at once. That is the whole point: a pocket calculator makes you retype the entire sequence when one number in the middle turns out to be wrong, and a phone calculator does not even show you what the sequence was.
Lines can refer to each other. `ans` is the line above, `line3` (or the short form `L3`) is one specific line, and `rent = 1500` gives a value a name you can use further down. Insert, delete or move a line and every reference is rewritten so it keeps pointing at the same line — renumbering never quietly changes a result.
A line containing just `total` adds up the expression lines above it, back to the previous `total` or the previous comment line — so one tape can hold several separate subtotals. Lines beginning with `#` are comments and act as those section breaks. Named lines (`rent = 1500`) are deliberately left out of a subtotal: they are inputs you refer to, not items in the list.
A quote written on the tape: `# Quote` / `860 * 3` → 2,580 / `1200` → 1,200 / `total` → 3,780 / `ans * 10%` → 378. Change the 3 to a 4 and the subtotal, the tax line and everything after it follow immediately. A tape holds up to 500 lines of 500 characters each.
Everything the calculator can compute
- Trigonometry: sin, cos, tan, sec, csc, cot; asin, acos, atan, atan2; sinh, cosh, tanh, asinh, acosh, atanh.
- Logarithms, powers and roots: ln, log10 (lg), log2 (lb), log(x, base), exp, sqrt, cbrt, root(x, n), and ^ for powers.
- Rounding and integers: abs, sign, floor, ceil, trunc, round(x, n), mod, gcd, lcm. Rounding is half away from zero, so round(2.5) is 3 and round(−2.5) is −3, and n may be negative: round(1234, −2) is 1200.
- Combinatorics and random: fact(n) (or the 5! suffix), ncr(n, r), npr(n, r), rand(), randint(a, b). Random values are seeded per line, so a result only changes when you edit that line — the tape does not reshuffle itself while you work further down.
- Lists: sum, count (n), mean (avg), median, mode, min, max, range, product, stdev (s), stdevp, var, varp, q1, q3, iqr, sem — so mean(12, 15, 9) works on one line without leaving for a separate tool.
Function names, along with pi, e, ans, mem, total and line7, are reserved: a variable cannot take one of those names, and the tape says so on the line instead of silently shadowing the function. Names are matched case-insensitively, and juxtaposition multiplies — 2(3+4) is 14.
Stats mode: the numbers and their definitions
Paste a column straight out of a spreadsheet — values separated by newlines, tabs, spaces, semicolons or commas are all accepted — and the panel reports n, sum, mean, median, mode, min, max, range, Q1, Q3, IQR, sample and population standard deviation, sample and population variance, and the standard error of the mean. Tokens that are not numbers are counted as skipped rather than silently dropped, so a stray header row is visible instead of invisible.
Quartiles use linear interpolation on the sorted values — R’s type 7, which is also what Excel’s QUARTILE.INC and Google Sheets return. Other conventions exist (Excel’s QUARTILE.EXC, Minitab, R types 1–9) and can differ by a noticeable amount on small samples, so a quartile that does not match another tool is usually a definition difference, not an error.
Divide by n − 1 for a sample and by n for a whole population: stdev is the sample figure and stdevp the population one, and both are shown so the choice is explicit. Outliers are flagged by Tukey’s fences — anything below Q1 − 1.5 × IQR or above Q3 + 1.5 × IQR — and the mode is reported only when a value actually repeats. Up to 100,000 values are read.
Angles, and where trigonometry stays exact
The DEG / RAD / GRAD badge is always visible because it is the single most common source of a wrong trigonometric answer: sin(30) is 0.5 in degrees and −0.988 in radians, and nothing about the number tells you which one you got. Changing the badge recalculates the whole tape rather than only the next line.
For the angles that have exact values, you get the exact value and not a rounded one: sin(30°) is 0.5, cos(60°) is 0.5, tan(45°) is 1, and sin(0), cos(90°) and tan(180°) are 0 — no 0.49999999999999994 and no 1.2246e−16. The ° suffix forces degrees on a single value, so sin(30°) stays 0.5 even while the calculator is in radian mode.
Everywhere else trigonometry, logarithms and roots are double-precision approximations — they have to be — and the result carries the ≈ mark so an approximate number never looks like an exact one. That mark is the calculator telling you the difference, which most calculators simply do not.
How results are displayed
In the default Auto number mode a fraction that cannot be written as a terminating decimal stays a fraction: 1/3 is shown as 1/3 with ≈ 0.333333333333 underneath, and 10/4 is shown as 2.5 because that decimal is exact. A result built from π keeps π in it — 2 × pi shows as 2π with its decimal below — so an exact answer is never lost to rounding on the way to the screen.
Two other modes are available. Decimal always shows a decimal, and Floating point shows the raw double the machine holds — which is how you see 0.30000000000000004 for yourself. Display precision runs from 4 to 14 digits (12 by default) and changes only what is drawn: the value behind it is untouched, and Copy gives you the exact value, including the fraction form when there is one.
Notation switches between standard, scientific and engineering (exponents in multiples of three, the form used on datasheets). And whenever a line could be read two ways — a percent, an implicit multiplication, a chain of powers — the tape prints the reading it used underneath, so you check a normalised expression instead of guessing at the parser.
Keeping, sharing and the limits
The tape is saved in this browser’s local storage, so closing the tab and coming back tomorrow does not lose it. It is not an account: the tape is not on any server, it does not follow you to another browser or device, and clearing site data removes it. Share link is the way to move a tape — or to keep a copy of one.
A shared link carries the whole tape, deflate-compressed, in the URL fragment after `#t=`. Browsers never send a fragment in an HTTP request, so a shared calculation cannot turn up in a server access log — not ours and not anyone else’s. Fragments are capped at 8,000 characters; a longer tape is refused rather than silently truncated.
Everything is keyboard-first: Enter commits a line, the arrow keys move between lines, and Ctrl+C copies the result of the line you are on. The on-screen keypad is there for touch, and on a phone it suppresses the OS keyboard while it is open so the two never fight over the screen.
Things people work out here every day
A bill with tax and a split: `24500 + 10%` gives 26,950, then `ans / 4` gives 6,737.5 per person. Because the tape keeps both lines, adding a fifth person is one edit, not a new calculation.
Unit price comparison: `4500 / 750` is 6 per gram against `7900 / 1200` at 6.583, and the two lines sit side by side instead of one having to be remembered while the other is typed.
A small budget with names: `income = 3200000`, `rent = 950000`, `income - rent` → 2,250,000, then `ans / 30` for a daily figure. Change `income` once and every line below it moves.
Marks, readings or measurements: paste the column into Stats for the mean, the median and both standard deviations at once, or stay on the tape with mean(88, 92, 79, 95) when there are only four numbers.