[ustolemyname]

That's like saying there's no difference between 99.9℅ the speed of light and going all the way there, from an engineer perspective. Turns out, one of these requires an infinite more expenditure of energy than the other. Similarly, if you're evacuating a tube by removing gave the gas at a time, 1/1000 is attainable. 0? Not so much.

[e2e8]

I don't disagree but that is not issue here. The issue is that for the purposes of discussing the mechanics of the tube like strength, seals, safety etc. the small amount of air left in the tube should not throw off simple calculations by too much.