Assumption cell

A labelled cell holding a single input, referenced everywhere it is needed and changed in one place.

Gathering the assumptions onto one sheet turns a model into an instrument. Sensitivity tables become possible, scenarios become a matter of switching a column, and a reviewer can see the whole set of judgements in one view.

The discipline also exposes how many assumptions a model actually contains, which is usually more than its author thinks.

If it can be argued about, it belongs in a cell.