Googled pt2 epr and came up with this as my first response....
Using our station numbering system, EPR is the ratio of nozzle total pressure pt8 to compressor face total pressure pt2. EPR can be easily measured on an ...
www.grc.nasa.gov/WWW/K-12/airplane/epr.html - 12k.
If I remember the JT3D correctly, a trick question in training was how did you anti ice the pt2 probe and how did you anti ice the pt7 probe
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