Guidelines:

- Formulae are short, simple, and easy to understand.
- Formulae are not atomised to the extent that they become difficult to understand in aggregate.

Complex formulae are difficult to understand – often even for the person that created them. Complex formulae are also more likely to have errors.

To reduce these issues, make formulae easy to understand.

## Make short formulae with few functions

We need to keep our formulae short and using few functions. A complex formula may need to be split into multiple steps, across several cells. That is, use "helper columns" (or rows) to do a complex calculation in steps rather than all in a single formula.

As a guide, any formula that is longer than 100 characters, or uses 4 or more functions, is a candidate for simplification.

## Trade-off between simple and atomization

However, there is a trade-off between the complexity of an individual formula and the aggregate complexity of a spreadsheet.

Dividing formulae into many small parts – atomization – leads to a proliferation of formulae and can result in long arcs of precedence (i.e., long sequence of cells in a calculation chain), which can be difficult to untangle. A highly atomised spreadsheet may be more difficult to understand than one that has fewer, slightly more complex formulae.

Seek a balance between formula complexity, atomization, and length of precedence arcs – with the goal of making the spreadsheet easy to understand, use, and change.