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xkcd #3094: Mass Spec
(imgs.xkcd.com)
Title text:
Patients at least found it to be an improvement over Millikan's incredibly messy and unpleasant oil drop suspension procedure.
Transcript:
[Ponytail, wearing a lab coat, is giving a balloon to Cueball. Behind Cueball, there is a ramp on the ground, a magnet hanging from the ceiling, and a target on a poster on the wall.]
Ponytail: Rub this balloon against your head, then go jump past that magnet toward the target on the wall.[Caption below the panel:]
Before the bathroom scale was invented, the only way to weigh people was mass spectrometry.
Source: https://xkcd.com/3094/
To make it a bit easier to measure the difference, you could do this in free fall or a micro gravity environment.
And a also a full vacuum. Your test subject might not look so hot after that, but science!
Air just gets in the way, in more than one way actually.