What does the preview show before I save?
This check is on New alert. The builder checks the rule against stored prices from the last 30 days. A mark shows each time the rule would have fired. The count for 30 days and the count for the last 7 days sit under the chart. The count is labeled Backtest, last 30 days, hypothetical, not a forecast.
Nothing is sent while you preview. Saving is what turns the alert on.
If there is not enough history, the preview says so, and you can still save. If the check does not finish, you can still save.
If the count is more than 30, the rule would have fired more than once a day on average. You can raise the wait, or raise the amount, before you save.
The preview uses the same rules as a live alert. It counts past hits. It does not say what the price will do next.