As far as my cranky old memory recalls,
it's just a NUMBER and is represented as a percentage of a fan rpm (the number of which is interesting but academic) nominated by the engine manufacturer as HPSOV and VnV suggest.
You could just as easily use numbers 1-10 to three decimal places like EPR, fruit machine pictures, coloured bands, or whatever turns you on. The actual thrust related to the number at any given point is whatever it is, given temp, and ambient presure and provided by the airframe/engine manufacturers.
The new FADEC systems have simple thrust lever settings like T/O, climb, crz etc.
What the engine is ACTUALLY doing, other than producing the commanded thrust and operating inside its parameters, is reasonably academic to the pilot.
Given that it has fuel availalable it's either operating correctly or you shut it down. There is little else you can do.
Whether the cockpit indicator uses USD's, zlotys or %age, it is simply that a relative indicator.
We are getting too close for my liking to the pilot and dog, flight crew scenario.
As Stamatis points out T/O thrust at ISA sea level at is delivered at 83% and as the aircraft climbs to less dense air the engine can accelerate towards a nominal limit of 100%. I guess a form of derate.
Either way all of the manufacturers have different ways of presenting and dealing with it.
[This message has been edited by gaunty (edited 24 September 2000).]