Down is from Headquarters (the division the train belongs)
Up is towards Headquarters (the division the train belongs)
e.g:- 06527 Down Banglore-New Delhi Karnataka belongs to South Western Division, hence it is Down, and its pair i.e 06528 Up New Delhi - Banglore Karnataka Exp is going towards its headquater i.e Banglore hence it is Up
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Members, Moderator plz correct me, if I am wrong