"Frequencies" tab page

There you can adjust launching frequencies of different rocket types. The most left slider position means lowest probability of launching rocket of such type. Actually, it will never be launched. The most right slider position will lead to most often launching the rockets of such type.

If you set two types to same frequency, this will mean that same quantities of rockets of both types will be launched.

FLAREDANCE Firework Screensaver configuration window screenshot: "Frequencies" tab