IN Hg ALg. MANIFOLD PRESS 35 50 10 15 25 40 30 20 45 35 50 40 30 45 IN Hg ALg. Manifold pressure sensing aneroid Capillary assembly Rocking shaft Frame Altitude compensating aneroid Figure 10-15.  An analog manifold pressure indicator instrument dial calibrated in inches of mercury (left). The internal workings of an  analog manifold pressure gauge are shown on the right. Air from the intake manifold surrounds the aneroid causing it to deflect and  indicate pressure on the dial through the use of linkage to the pointer (right).  gauge compares the total exhaust pressure to the pressure  of the ram air at the inlet of the engine. With adjustments  for temperature, altitude, and other factors, the EPR gauge  presents an indication of the thrust being developed by  the engine. Since the EPR gauge compares two pressures,  it is a differential pressure gauge. It is a remote-sensing  instrument that receives its input from an engine pressure  ratio transmitter or, in digital instrument systems displays,  from a computer. The pressure ratio transmitter contains the  bellows arrangement that compares the two pressures and  converts the ratio into an electric signal used by the gauge  for indication.  [Figure 10-16] Fuel pressure gauges also provide critical information to  the pilot.  [Figure 10-17]  Typically, fuel is pumped out of  various fuel tanks on the aircraft for use by the engines.  A malfunctioning fuel pump, or a tank that has been  emptied beyond the point at which there is sufficient fuel  entering the pump to maintain desired output pressure, is a  condition that requires the pilot’s immediate attention. While  direct-sensing fuel pressure gauges using Bourdon tubes,  diaphragms, and bellows sensing arrangements exist, it is  particularly undesirable to run a fuel line into the cockpit,  Fuel Pressure 10-10 Figure 10-16.  Engine pressure ratio gauges.  PRESSURE RATIO 3.4 1.2 1.5 2.5 3.0 2.0 0 8 6 4 A. An analog EPR gauge  from a turbine engine C. Engine pressure  ratio transducer B. A digital EPR indication and other turbine engine  parameters on a cockpit digital display screen 1.02 1 1.4 1.8 24.0 6 10 330 1 1.4 1.8 24.0 6 10 EPR EGT °C FF KG/H 540 N3 % 17.3 FF KG/H 800 N3 % 55.3 FOB: 28000 KG N1 %