When you move the throttle in all jets - 727, 707, 747 etc. you are sending a command to the FCU (fuel control unit) on the engine. In the older planes that was accomplished by a cable and push-rod arrangement. On the newer jets -except Airbus - the command is via wire (potentiometer) to the FCU. The result is the same. In the Airbus the command is sent to a computer first which decides what the engine does. That is not to say that the FCU does not make adjustments, it does, but the computer part of the "Bus" is more controlling.

EPR is the primary thrust setting instrument with N1 being secondary. The resulting FF can vary depending on the condition of the engine. A newer engine may have a lower FF just because it is tighter. Same with EGT. The newer engine could have a lower EGT for the same power since its just working better.

Jets are designed to work better at high altitudes and colder temps. In the old days the "straight pipe" non fan did great at high altitude, but was less stellar at lower altitudes. With the advent of the by-pass fan, low altitude performance was much better. Today, with the huge fans the efficiency of the power plants is at an all time high. A lot of thrust at low altitude and great performance at cruise altitude.

When you set cruise power, you must be at the correct speed when you set the EPR. If you are faster when you set the EPR, the engine is actually producing more power for the same EPR. Same is true if you are slower than proper cruise speed when set EPR the engine is not producing the correct value. Once the F/E would set cruise power, they would wait a bit for the engine to stabilize and then see how the speed is holding. If the speed held, then the F/E could take readings of all the engines and compare the condition of each engine. With the same EPR set in each engine, the N1 & N2 speeds along with EGT and FF would give a pretty good comparison of the engine to chart values.

Lou