Evidence and data quality
4 min read · Updated 23. September 2026
A report without evidence is a list of claims. While nobody checks it the difference is invisible; the moment a bank or a customer asks where a number came from, it shows in a minute.
What counts as evidence
- A supplier invoice for electricity, gas, heat or fuel — the ordinary and the strongest source.
- A meter reading with a photo or a printout, when the invoice for the period has not arrived yet.
- A service report for cooling systems: how much refrigerant was topped up, and which one.
- An internal record — a spreadsheet of kilometres driven, say — when there is nothing else. It is evidence, but weaker, and that has to be said.
Measured, calculated, estimated
Every figure is one of three. Measured comes off a meter or an invoice. Calculated is derived from something measured by a known rule: litres from kilometres and average consumption. Estimated is everything else. An estimate is not forbidden and is often the only option in the first year; what is forbidden is letting it look measured.
How to write it down
Next to every row, record where it came from: the invoice number, the reading date, the service date. If it is an estimate, say how you arrived at it — «three months averaged and multiplied by twelve» is enough. A year later nobody reconstructs that from memory, including you.
What it buys you
- An answer in a minute when somebody asks for the source.
- Comparability between years. If last year was an estimate and this year is an invoice, a change in the number may be the method rather than the consumption — and you need to be able to show that.
- Less work next year. The sources are written down, so the second year does not start with a search.
How long to keep it
Keep the invoices and records a report is built from at least as long as the report itself stands, and in practice together with the accounting documentation. A report that points at evidence which no longer exists is worse than one that never promised any.