If EPR 1 equals zero thrust (which is not idle for a jet) how come have I seen EPR of 0.9-1.0 in the cruise? RR Trent 772 I think.
In some installations, EPR actually has a deducible meaning and can be used with rules-of-thumb. On things like the Trent, it appears to be just another random number with EPR<1 giving net thrust.
Much easier to look at N1 which is what most of the tables in the QRH use, funny old thing!
EPR also changes markedly with altitude & temperature, which makes it difficult to perform quick sanity checks on things like T/O thrust unless you're the Lucasian Professor of Mathematics...