A pilot's star rating is computed based on the pilot's usage during the previous 90 days.
1 star = 1 hours / month
2 stars = 2 hours / month
3 stars = 3 hours / month
4 stars = 4 hours / month
5 stars = 5 or greater hours / month
The rating metric is driven by the bookable resource timer configuration. For example, the TACH meter may be configured to drive the star rating, whereas the LANDINGS counter would not be included in the calculation.
Reference: Timer Reporting Features.