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At 03:55 PM 11/1/2013, John Schroth wrote:
>Is there a measurement device that could tell you if your heads require 
>demagnetization?

The most sensitive "measurement device" I've found is a reel of carefully 
bulk-erased tape and the human ear.  The tape noise sounds quite different 
after the tape has passed over a magnetized object.  Noise of the 
bulk-erased tape is nice and smooth.  Noise with even a small amount of DC 
magnetization sounds much rougher.  Easy to remember once you've heard 
it.  Or, record the tape noise just after the machine has been 
demagnetized, and save the file for comparison with later playback of the 
bulk-erased tape.  If the quality and level of the noise match the 
reference file, your machine is not magnetized.

This test is much more sensitive than any hand-held magnetometer that I've 
ever seen.

-- John Chester