The number in Magnet is a Static CPR number. It represents the estimated number of promotional sales for a product you need in order for it to rank on page one for a keyword. This score is proprietary, taking into account various attributes of the keyword and the products that rank for it.
Keep in mind that the 2021 CPR Score only applies to those keywords in which your product does not currently rank on the first page (ranks position 1-16 in a keyword’s search results) at the time of the search. Helium 10 also has its Dynamic CPR score, available in Keyword Tracker.