Hi Amer, Avian, Chess et al,
Notwithstanding the Pioneer and H/K attempts to establish some kind of reference level, I do find this "calibration" of the front-panel readouts rather arbitrary and, for many users, counter-intuitive.
It stems from audio broadcasting standards, where "0 VU" on a standard VU (Volume Unit) meter on the control-room console actually was a standard calibrated level, so feeds from studios in different cities or locations would always be at the same level.
Above that 0-dB level, +3 dB indicated a distortion level of 1%, if memory serves.
But unless you clearly understand the logarithmic relationship of the decibel, it's confusing for consumer use.
By the way, amer, in acoustic sound pressure levels (SPL), it requires a 10-dB increase in sound levels to subjectively "double' the apparent volume. This requires an electrical increase of ten times. If a speaker needed 5 watts to produce a sound level of 90 dB SPL at 1 metre, and you wanted to subjectively double the volume, you'd need to supply 50 watts to the speaker to increase its acoustic output to 100 dB SPL. That's why slight differences in the rated power output of an amplifier really aren't very meaningful.
Axiom Resident Expert