How we measure

How often does the engine set change and what happens to your history?

The engine set changes rarely, and only when an engine can be measured faithfully or can no longer be. It currently holds 8 engines. When it changes, your history is not rewritten: past runs keep the engines they were actually collected on, and a new engine starts its own series.

Backfilling a new engine into old dates would be the convenient move and it would be fiction. Nobody collected that engine in March, so March cannot have a reading for it.

The practical consequence is that a comparison spanning an engine change needs care, and the product says so where it matters rather than letting a step in the chart read as a real movement.

Removal works the same way in reverse. Historical readings for a retired engine stay in place and are labelled as ended, because deleting them would silently rewrite every total that included them.

What this answer is based on

AI engine registry — the measured engine set and its change log