Tithe Grade refers to the amount of materials an Imperial world must supply to the Administratum. The size of the tithe depends on the type of world it is applied to. A tithe can be any form of material: food, weapons, minerals, people, etc.
Space Marine homeworlds do not normally have tithes, and are given the tithe grade Adeptus Non.
Agri World tithes generally refer to how much of the planetary production must be supplied.
Known Tithe Grades1
- Adeptus Non (also Aptus Non)
- Solutio Tertius
- Solutio Prima
- Solutio Extremis
- Decuma Particular
- Exactis Tertius
- Exactis Prima
- Exactis Particular
- Exactis Extremis
Source
- 1Warhammer 40,000 3rd Edition Rulebook, pp. 114–115