What is going on inside my magnets?

Hi All,

I'm currently trying to make a diamagnetic levitation system for manipulating microdroplets for my Ph.D. As I was carefully grinding down my magnets to an appropriate size I noticed that the strength of the field didn't change that much. One magnet before the grinding produced a maximum magnitude of ~0.46T and after grinding the field on the same side produced a maximum magnitude of ~0.45T! I measured the field with a Teslameter and ground down the magnets using a file and ethanol for cooling.

Can anyone explain this to me (I'm only a self-taught physicist)? I'm thinking it's something to do with the magnetic domains....

Thanks