He did. It's a ratio. If you know atmospheric pressure, you can plug it in to get maximum allowable boost.
Thank you!!!
This is what i was after.
It explains everything.
I was on to it.
Atm pressure is 983mbar here
0.983 x 2.09 is about 2.1 bar absolut, which gives us 1.1 bar of boost or 16psi.
That should be just right??