Think about what a spreadsheet actually is at heart: a grid of cells, each holding some value. A cell can hold a plain number, some text, or — and this is the interesting case — a rule for computing a value from other cells. That rule is a formula. The whole power of a spreadsheet comes from the fact that you describe the relationship once, and the machine keeps re-evaluating it forever.

The intuition

Suppose you run a small shop. You put the price of an item in one cell and the quantity sold in another. You want the total. You could just type the number you worked out on your calculator — but then the moment the price changes, your total is a lie. You'd have to redo it by hand, every time, for every row.

A formula flips this around. Instead of storing the answer, you store the instruction: "take whatever is in the price cell, multiply it by whatever is in the quantity cell." The spreadsheet holds the recipe, not the cake. Change an ingredient, and the cake is baked again automatically. This automatic re-computation is the single most important idea in the entire subject — everything else is detail on top of it.

The precise statement

A formula is an entry in a cell that begins with an equals sign =. That leading = is the signal that tells the spreadsheet: do not store this text literally; evaluate it as an expression. Everything after the = is an expression built from three kinds of ingredients:

• Numbers — literal constants like 5, 3.14, -20.
• Cell references — addresses like A1, B7, C12, which stand for the current value of that cell.
• Operators — symbols that combine the above into a calculation.

The arithmetic operators are:

So =A1 * B1 means "multiply the value in A1 by the value in B1." The cell displays the result of that multiplication, but what it actually stores is the formula. Click the cell and you see the formula in the formula bar; look at the cell itself and you see the number.

Why the result updates automatically

This is the payoff. A cell reference is not a copy of a value; it is a live pointer to another cell. When you change the value in A1, the spreadsheet does not wait for you to ask — it re-evaluates every formula that depends on A1, then every formula that depends on those, and so on down the chain. This cascading re-evaluation is called recalculation, and it happens the instant you commit a change.

Concretely: if C1 contains =A1 * B1 and you edit A1 from 10 to 12, then C1 immediately shows the new product. You did nothing to C1. That is the behaviour you are buying when you write a formula instead of a number.

Order of operations

When several operators appear together, the spreadsheet follows the standard mathematical precedence, not left-to-right reading order: …