I like to give the benefit of the doubt. Although improbable, maybe they're measuring the level of static buildup on the head arm, with relation to ground, in a HDD design lab. Things spinning at great speed are known to generate static.
@b_force: to quote your sig back to you, consider this as a possibility: ""If you can't explain it simply (or at all), you don't understand it well enough." A. Einstein
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