It's a real gauge. The answer to your question will be in your Owner's Manual...seriously...my 1990 Toyota has tick marks that correspond to minimum pressure at hot idle, at cold idle, hot running, etc....and the manual has that detail...
That detail is all I've ever needed in 240,000 miles of running. In the summer, when 4 Wheeling and the engine is good and hot, 10W30 keeps it just above the hot idle tick when idling. 5W40 keeps it a bit farther above that tick in the same conditions. (OM allows for 5W30 winter, 10W30 or 10W40 summer) Pressure is well above the running tick mark with either viscosity, so, I know that my oil pressure is correct/sufficient without knowing the PSI...and the gauge still works perfectly, 23 years later.