"Richard J Kinch" wrote:
Ignoramus26567 writes:

What does your pressure gauge show when your compressor tank is open,
0 or 14.7?

How much pressure does an open tank hold, if you say atmospheric pressure
is zero?

Zero, of course; pressure is measured as a differential, just like voltage.

Now, if you take that empty tank at zero pressure, cap it up, and fling it
into space, *then* it will be at 14.7 PSI.

Jon