The Magician's Tower

Wondering what the minimum pet level on the focus items means. Is that for the caster or the pet level?? For instance, will the OS AVUS EMXXIII work on my level 100 mage pet or BL pet?? For my BL would I have to get my level 103 pet to use this focus?? Thanks!!

Assuming it works like every other focus, it's the level of the spell.