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Ideally you want 1.e-6 (one millionth) torr.
A torr is 1/760 atmosphere. For ordinary tubes
1.e-4 torr is not "gassy" but a CRT would not like that.
1.e-2 torr of air will give a nice purple glow,
not bright but there.
The pumps used in processing will easily do 1.e-6 torr
at their inlets ... but its not easy to get that through the glass stem.
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