David Billington wrote:
It would be interesting to know what granite was used for the base of
your height gauge. The black granite I have about shows no magnetic
attraction at all when NiFeBn magnet is placed on it. As granite is
predominantly SiO2 it would be interesting to know why the magnetic
attraction.

Given the strength of these magnets I could believe it was just being
attracted to a steel fitting in the centre of the height gauge base. Is
this possible, or was it definitely being attracted to the granite?

Chris