It is an average across every impression, so it moves when the mix of queries moves. Ranking newly for a long-tail phrase at position 30 lowers your average position while being unambiguously good news.
This is the only source of position data in the product. We do not scrape search results, and placement inside an AI answer is reported in its own unit rather than being folded into this one.
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No card, and the free tier does not expire — the first verdict takes about six weeks to arrive.