Center gauge is a torque gauge, rather than a boost gauge, if in fact the gauge is stock. No idea if these gauges also use stepper motors. Maybe Dragon2U has an answer for you.Boost gauge?
I don't believe this is stock.
Does you SSR have a supercharger or turbocharger.
Did it ever work ? If not and if it does indeed say boost gauge and no supercharger, I would suspect previous owner had a supercharger that they removed before selling.
Just some of my thoughts.