This!Serious evaluations must be at exactly the same level as determined by instrumentation. Not doing this is probably the number one mistake of hobbyists (and some "scientists" too).
Except you should have typed EXACTLY
And checking that with an SPL meter is bull****, that is way too subject to other vagaries. Voltmeter or die.
Working for a $3 billion audio company, argh the @#$%'ed up listening tests I was forced to attend. With volume not even compensated, or in some cases (different head units for example) you simply could not match the level exactly due to volume control steps. Another time we had a Tripath amp chip inside a head unit, and again the gain was just different. But any equipment with a 1 dB volume adjustment will show how sensitive we are to level, especially if the volume is not so high and thus we are into the loudness curve of our hearing.