Got this Gaussmeter because (1) it has the same probe connector as the Walker Scientific MG-3D Gaussmeter (which does not properly zero) and because (2) there is a free on line manual for the Bell 640.
The most sensitive range is 100 milli gauss full scale ( 1 mG per division) up to 30,000 G full scale. Compare to the Earth's magnetic filed (Wiki) of about 0.5 Gauss. So this meter is of no use for finding North or magnetic compass work, but is useful for measuring permanent and electro magnets.
The word "Incremental" in the instrument name is because the zero controls allow nulling any field up to full scale.
DC Permenant Magnet Motors
Walker Scientific MG-3D Gaussmeter
AlphaLab Inc DC Gaussmeter Model 1
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