Is there any device to measure the force between two magnet?
The force between two magnets depends upon the geometry of the magnets, and their relative positions:
But if you can constrain their motion - put two bar magnets into a tube - you can use a simple force scale to measure the push/pull. For really close work you would use a piezo crystal, but an ordinary spring scale will work.
Pull spring scales: http://www.globalindustrial.com/g/packaging/scales/Dial/spring-scales-99102
Or a load cell: http://www.futek.com/product.aspx?t=load
Or you can just hang some weights ... and see how much it takes to break the magnetic grip. Slip something between the magnets to control the spacing.
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