Simple Forecast Model Builder

Help me build a simple {{forecast_type}} forecast in {{spreadsheet_app}} for {{business}}. Historic data available: {{historic_data}}. Horizon: {{horizon}}.

Provide: the sheet layout (inputs, calculations, outputs); each key assumption listed in an input cell with a source or rationale; the formulas for each row; base, optimistic and pessimistic scenarios; sensitivity to the 3 biggest drivers; sanity checks (does it reconcile to history, are growth rates plausible); and the limitations of this approach. Make the model transparent so a non-expert can audit it, and avoid false precision.