When you upgrade you get the additional number of boomerangs that will bring you to the total number of boomerangs you should have at a given package.
You are at Standby with 5 Boomerangs.
You upgrade to Coach.
Coach is supposed to have 10 Boomerangs in total.
So when you upgrade from Standby to Coach, you get 5 additional boomerangs which brings you to 10 total.
Boomerang Upgrade Amounts*:
- From Standby to Coach Class = 5
- From Standby to Business Class = 20
- From Standby to First Class = 45
- From Coach to Business Class = 15
- From Coach to First Class = 40
- From Business Class to First Class = 25
* Amount shown is the number of additional boomerangs you get when you upgrade