where:

..\Images\IMG00142_shg.gif

is the location of the inlet face.

..\Images\IMG00143_shg.gif

is the location of the engine face.

..\Images\IMG00144_shg.gif

is the area of the inlet face.

..\Images\IMG00145_shg.gif

is the area of the duct cross section at station ..\Images\IMG00146_shg.gif .

..\Images\IMG00147_shg.gif

is the perimeter of the duct cross section at station ..\Images\IMG00148_shg.gif .