Ultimately the housing will have a centre of gravity and when it goes up and down you can approximate the whole item to a single point. In absence of external forces the housing will not rotate around its centre of gravity. If you induce a force and make the item rotate on an axis this will continue to spin.
This makes absolutely no sense. Did I miss a smiley?
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Typos are a feature, not a bug
When people say the macro port makes the rig heavy in the front or the acrylic dome makes the rig light in the front is because the centre of gravity moves and now you have a torque on the axis between the handles of the rig if the overall system is negative or positive. When the rig is neutral it will stay in any position you leave it so if you are within grams this doesn't really matter much. In most cases though rigs are around 1 pound negative or less but not really 0.
So to have a perfectly balanced rig you need to ensure that the centre of gravity is on the axis between your two hands. Inducing an additional vacuum of 200-300 Mbar over a rig of more than 5 kg such as the gates housing in the clip will have an effect of few millimetre in determining the centre of gravity and therefore will be completely irrelevant