Engine oil pressure, and temperature.
The 3rd ?? How about hydraulic steering, water pressure, or perhaps ‘steam pressure’ when the skipper ‘loses it’ !?? The two pressure gauges have different scales, I don’t think engine oil pressure would go to 10Bar without something going bang. On my 331 the 3rd gauge is engine revs.
I guess the answer lies in tracing the wiring/tubing back to a sensor ?