CHT and EBF books are controlled by parameters as found in the personal/prodeo.eng configuration file.
[EBF File = books\2016.ebf] * database location
[EBF Depth = 30] * consult EBF database till 15 moves
[EBF Priority = CHT] * EBF | CHT
[CHT File = books\2016.cht] * database location
[CHT Use = all] * human | comp | all | none
[CHT Priority = comp] * human | comp
[CHT Depth = 60] * consult CHT database till 30 moves
For the meaning of the CHT parameters we refer to Prodeo 1.84.
The [EBF Priority = ] parameter decides which book should be used as first one. For the moment the CHT book performs better and thus the CHT setting is used. When a move is found in the CHT book it is played, if nothing is found it will consult the EBF book. Using the setting EBF will reverse the search order.