There's also the "Suppress Non-Hold Transits Group" library setting, which could be used to make entire library collections effectively "float". The circ lib wouldn't be automatically changing, but the items wouldn't be springing home either.
This creates lots of items belonging to Library A (with circ_lib of A) but staying at Library B with Available status. You really don't know where the items are from the catalogue.
Tina Ji 1-888-848-9250 Trainer/Help Desk Specialist BC Libraries Cooperative/Sitka
