Number checking

Recompute every figure that matters, by hand or in a sheet. Language models are fluent about arithmetic in a way that is genuinely misleading — the working can be laid out perfectly and still arrive at the wrong number, and the presentation gives you no signal either way.

Then check the assumptions inside the calculation, which is where the larger errors live. A growth rate applied to the wrong base, a percentage of a percentage, a currency conversion at an unstated date. Write down the assumption you had to supply yourself to make the number work — if you had to supply one, that is a finding.