Field help (OBCLDR) 

The master object is the object on which the recoding is mainly carried out. This setup is applied when the status of the former codes has for value: Stored or Inactive.

SEEINFO The Physical count lists and Physical assetsobjects cannot be master objects.
The selection terms of the different object recordings depend on the choice of the master object. These terms are described in the help of the Mass recodings function.