The game pressure is measured in units up to 255, I don't think it is a real value. But I'm not sure. (I'm also saying this because there is negative units, which don't occur in real life.)
they don't need to have an actual value, seeing as it is a game.... but the heat is a nice thing to have realistically, speaking of which, the plasma should have a heat value of 115, and thats conservative, helium plasma would have one of 20.