It was taught as psia, -g, & -d (or absolute, gauge, and differential) when I was in school, so I read your -1 atm as psid. Your car example would be 32 psi gau

It was taught as psia, -g, & -d (or absolute, gauge, and differential) when I was in school, so I read your -1 atm as psid. Your car example would be 32 psi gauge assuming STP, or ~36 psi absolute. The miners are below the surface and not at 1 atm, so any gauge measures taken there would be psid.