system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: I read today that the SpaceX space suit was tested to double vacuum pressure. If a vacuum is zero, then how can it be doubled?
gpt
A single vacuum pressure is when you have a vacuums worth of pressure on one side and an atmospheres worth of pressure on the other. 

If they double this, this means they had double atmospheric pressure on one side and a vacuum on the other.