Arcla
What Notso Fantastic may have been trying to say is that N1 is just a percentage of rotational speed. EPR is the ratio of inlet to outlet pressure. As both engines get older the N1 percentage remains the same but the output of the engine deteriorates. This isn’t presented to the crew. An engine that measures its performance with EPR won’t be able to deliver the same performance as a new engine. The EPR gauges will show this to the crew as a lower EPR value.