The reactive page
CALCULA is not a single-screen calculator: it is a page where you write your calculations one under another, as on a sheet of paper. Each cell is a calculation, and the cells talk to each other.
One cell, one calculation
Click in a cell, write an expression, end with =: the result appears faintly, to the right of the equals sign, before you have even confirmed it. Enter confirms the calculation and moves to the next cell — there is no button to hunt for.
Everything is saved as you go, in your browser. Closing the tab loses nothing.
A cell that defines a variable
A cell of the form m = 2.5 computes nothing: it defines. The symbol m becomes usable in every cell that follows, exactly like a given in a problem statement.
This is where the page becomes reactive: go back to the first cell, replace 2.5 with 3, and p recomputes on its own. Nothing to re-run. The Variables tab of the second screen shows at all times what the document has defined, with up-to-date values.
A unit is part of the value: m = 2.5 kg propagates through the calculations and the result carries the compound unit. See the guide on units and uncertainties.
What happens under the result
Two collapsed panels accompany every result:
- Steps — the breakdown as you would write it by hand: the starting formula, the substitution, the intermediate calculation, the result.
- How? — what the machine actually did: the exact expression the engine received, the algorithm used, the duration. This is what you read when a result surprises you.
The “Steps open” setting (⚙ Settings) unfolds them by default for the whole document.
Pages, rows and columns
“Add a row” adds a row, and a row can hold several cells side by side — handy for lining up measurements. “+ page” adds a page; the orientation (portrait / landscape) is chosen per page, and matters for the PDF export.
Try it: the “Error propagation (lab)” template
“From a template” ▸ Error propagation (lab). The document defines L = 1.250 ± 0.002 and T = 2.24 ± 0.03, then computes 4π²L/T². Change T to 2.20: the g you get moves immediately, its uncertainty with it, and the Steps panel shows the substitution.
Where to go next
The “≡ Selection” button on each cell opens what can be done with what is written in it: see formulas and chains. For a calculation no formula describes, there is the Python cell.