+// Return the sea level pressure for a metar observation, in inHg.
+// This is different from QNH because it accounts for the current
+// temperature at the observation point.
+// metarPressure in inHg
+// fieldHt in ft
+// fieldTemp in C
+
+static double reducePressureSl(double metarPressure, double fieldHt,
+ double fieldTemp)
+{
+ double elev = fieldHt * SG_FEET_TO_METER;
+ double fieldPressure
+ = FGAtmo::fieldPressure(elev, metarPressure * atmodel::inHg);
+ double slPressure = P_layer(0, elev, fieldPressure,
+ fieldTemp + atmodel::freezing, atmodel::ISA::lam0);
+ return slPressure / atmodel::inHg;
+}
+