They don’t say much, stuff about experiments material design and more experiments.
The store listing conversion rate also matters.
And they also mention that the top charts are for a period of 7 days, except the top free and trending that are being reset after 30 days.
Here is the video for you guys : https://www.youtube.com/watch?v=j33M5BqoLuI&index=10&list=PLWz5rJ2EKKc8jQTUYvIfqA9lMvSGQWtte