Figure 10-13  shows the instrument face of a typical oil  pressure gauge of this type. Digital instrument systems use  an analog or digital remote oil pressure sensing unit that  sends output to the computer, driving the display of oil  pressure value(s) on the aircraft’s cockpit display screens.  Oil pressure may be displayed in a circular or linear gauge  fashion and may even include a numerical value on screen.  Often, oil pressure is grouped with other engine parameter  displays on the same page or portion of a page on the display.  Figure 10-14  shows this grouping on a Garmin G1000 digital  instrument display system for general aviation aircraft. In reciprocating engine aircraft, the manifold pressure gauge  indicates the pressure of the air in the engine’s induction  manifold. This is an indication of power being developed by  the engine. The higher the pressure of the fuel air mixture  going into the engine, the more power it can produce. For  normally aspirated engines, this means that an indication  near atmospheric pressure is the maximum. Turbocharged or  supercharged engines pressurize the air being mixed with the  fuel, so full power indications are above atmospheric pressure.  Turbine engines have their own pressure indication that  relates the power being developed by the engine. It is called  the engine pressure ratio (EPR) indicator (EPR gauge). This  Most manifold pressure gauges are calibrated in inches of  mercury, although digital displays may have the option to  display in a different scale. A typical analog gauge makes  use of an aneroid described above. When atmospheric  pressure acts on the aneroid inside the gauge, the connected  pointer indicates the current air pressure. A line running  from the intake manifold into the gauge presents intake  manifold air pressure to the aneroid, so the gauge indicates  the absolute pressure in the intake manifold. An analog  manifold pressure gauge, along with its internal workings, is  shown in  Figure 10-15 . The digital presentation of manifold  pressure is at the top of the engine instruments displayed on  the Garmin G1000 multifunctional display in  Figure 10-14. The aircraft’s operating manual contains data on managing  manifold pressure in relation to fuel flow and propeller  pitch and for achieving various performance profiles during  different phases of run-up and flight. Engine Pressure Ratio (EPR) Manifold Pressure Figure 10-14.  Oil pressure indication with other engine-related parameters shown in a column on the left side of this digital cockpit  display panel.  10-9