Spreadsheet
Values, formulas and what-if
Make a sheet that recalculates itself.
A sheet holds two kinds of values. A basic value is typed in, such as quantity (Q) and price (P). A derived value is worked out from others, such as value V = Q × P. Labels are text, like headings; they describe, and they cannot be calculated.
A formula is an expression that works on values in cells. Remember the rule: every formula starts with =. It usually refers to other cells: =A1+A2+A3 adds three cells. The cell shows the result; the formula bar shows the formula behind it.
Excel follows the same order of operations as algebra:
- Brackets first.
- Then exponents (powers).
- Then multiplication and division, left to right.
- Then addition and subtraction, left to right.
You may know this as PEMDAS, BEMDAS or GEMS.
Because derived values update by themselves when a basic value changes, a sheet can answer 'what if?' questions. Type in a deposit, a rate of interest and a period; change the rate, and the maturity amount and compound interest change at once. This is a what-if scenario.
Alan Kay's value rule: a cell's value depends only on its own formula, and working it out has no side effects on any other cell.
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