[Amps] "Tubes 201" - How Vacuum Tubes Really Work

[S. J. Blackwell]

>Peter,
>
>I don't think he said they absolutely couldn't happen. What I've read about 
>this was that the most vacuum that can be pulled is around 10 atmospheres.

Can someone explain to me what 10 atm of vacuum is? I have always thought in 
terms of absolute pressure. Back in the mid 20th century, when in college,I 
participated in the construction of a mass spectrometer. We used a 
mechanical fore pump and a Hg diffusion pump with a cold trap. The numbers 
we thought seemed approiate were examp: 1x10-12 mmHg pressure. 10atm of 
vacuum does not compute for me. Did I miss something?
73,
Sam, W5LU