The Plot guide

Plot turns your readings into an honest graph. This guide follows one real experiment — a swinging pendulum — from the first stopwatch reading to a finished graph with error bars and a best-fit line. Every part works the same way for your own experiment.

Entering your data

The table works like a spreadsheet. Click a cell and type a number. Press Enter to move down, or Tab to move right. You can also copy a block of numbers in Excel or Google Sheets and paste it straight into the table.

The Plot data table: a column of lengths and a column of times, with the row numbers on the left. — The data table. Each column is one variable; each row is one reading.

Every column is a variable. The variable you change on purpose (like the length of a pendulum) is your x-variable. The variable you measure (like the time it takes to swing) is your y-variable. Open the x-var or y-var tab on the right to give each variable a name, a symbol and a unit — the symbol and unit appear on the column header and on the graph's axes automatically.

Tip: the + button next to the variable tabs adds another variable. The bin icon deletes one.

Typing ², ₀ and Δ

You don't need to know any keyboard tricks. Click into a name, symbol, unit or formula field and a small character bar appears just below it. Click a character — ², ₀, Δ, θ and friends — and it is typed into the field for you.

The character bar under a symbol field: superscript digits, subscript digits, and Greek letters. — The character bar. The top row makes superscripts, the bottom row makes subscripts and Greek letters.

In a formula you never need the special characters: ^ means "to the power of", so t^2 and t² calculate exactly the same thing.

Repeated trials

Good experiments repeat each measurement. In the pendulum experiment you might time 10 swings three times for every length. Plot can hold all three readings and work out the average for you:

Open the y-var tab and pick the variable.
Tick Enter as repeated trials and choose how many trials.
The table jumps to a new sheet with one column per trial. Type your readings there.

A trials sheet: three trial columns of stopwatch readings, the computed mean column, and the computed uncertainty column. — A trials sheet. Plot computes the mean and the uncertainty — those two columns fill themselves and can't be typed in.

Plot writes the mean into the variable's own column, and can use the spread of your trials as the uncertainty — either the half-range (max − min) ÷ 2, or the standard error. Use the sheet tabs under the table to switch between the Overall table and each trials sheet.

Calculated columns

Often the thing you measure is not the thing you plot. In the pendulum experiment you measure the time for 10 swings (call it t₁₀), but the theory says to plot T² against length. A calculated column does that arithmetic for you, for every row:

Add a new y-variable with the + button.
At the top of its card, change Raw data — typed in to Calculated — from a formula.
Type the formula, using your other columns' symbols: (t₁₀ / 10)^2.

A calculated variable's card: the data-type dropdown set to Calculated, and the formula field showing (t₁₀ / 10)^2 with the symbol coloured. — A calculated column. Symbols you reference are coloured, and the column's cells fill themselves.

The column fills in instantly and updates whenever your raw data changes. Its cells are read-only (they show a small ƒ in the header) — click the column header any time to jump back to the formula.

What you can type in a formula

Your other columns, by symbol: t₁₀, L, V…
The operators + − × ÷ ^ (the ordinary * / work too) and brackets.
Functions: sqrt (or √), ln, log, exp, sin, cos, tan, abs — angles in radians.
The constants pi (or π) and e.

Good to know: in a formula, a symbol always means a column. If your column is literally named x², typing x² refers to that column — to square the x column instead, type x^2. Plot colours each symbol it recognises, so you can see exactly what the formula is reading.

If a formula has a problem — a symbol Plot doesn't know, or two formulas that point at each other — the column shows blanks and a short note under the formula explains what to fix. Nothing breaks; nothing is lost.

Error bars

Each variable chooses where its uncertainty comes from, in the ± dropdown on its card:

Fixed ± — one value for the whole column, like a ruler's ±0.05 cm.
Per-point (Δ column) — a different value for each row. Plot adds a Δ column next to your data for you to fill in.
Calculated from trials — the spread of your repeated trials (see above).
Carried through the formula — for calculated columns. Plot recalculates the formula at each input's ± limits and uses half the spread, so your T² inherits an honest uncertainty from your stopwatch readings.

Error bars appear on the graph automatically once a plotted variable has an uncertainty.

The best-fit line

On a variable's card, under Fit, choose a model — a straight line, or a curve (exponential, logarithmic, power, quadratic). Plot draws the best fit and shows its equation on the graph; the gradient, intercept and R² appear in the results bar at the top.

The pendulum graph: T² against L with error bars, a best-fit line, faint maximum and minimum gradient lines, and the fit equation. — The pendulum result: a linear fit with error bars and the max–min gradient lines. The gradient of this line gives g.

For a straight-line fit you can also show the maximum and minimum gradient lines — the steepest and shallowest lines that still pass through your error bars. That gives the gradient's own uncertainty, m ± Δm, the way exam boards ask for it. Turn it on with Exclude outliers from fit and the Δm method dropdown.

Tip: drag the equation label anywhere on the graph. Double-click it to send it back to its automatic spot.

Saving and exporting

Your graph: the File button (bottom-left rail) exports a crisp SVG or PNG, or prints straight to PDF — clean enough for a printed report.
Your data: the same menu exports the whole table as CSV for Excel or Sheets, or downloads the entire lab as a file you can open again later on any computer.
Signed in: press Save in the left rail and the lab lives in your cloud workspace — open it from any device, insert its graph and table into a Write report, or hand it in for an assignment. If you open the same lab in two places, Plot warns you before one copy can overwrite the other's saved changes.

Signed out, Plot also keeps your current session in this browser automatically, so closing the tab doesn't lose your work.