Head Office Overheads Sheet
Actual evidence first, formulae second.
Hudson and Emden formulae, applied properly. Actual evidence is the strongest route and sits above both, so the sheet runs all three: evidenced head office cost for the period, then the two formulae as approximations, with the lost-opportunity evidence every route needs to turn arithmetic into a loss.
What you get
An Excel template with no macros. Only the yellow cells can be edited, the Guide tab explains every step, and it prints on A4. Your contract's terms come first.