You're being entirely arbitrary in your definition of what constitutes a measurement device. You seem to be hung up on intent.
What I'm trying to focus on is that a measurement (i.e. measure, number) has to be invented. They get invented when an experimenter needs a new way of thinking about a problem. Volts, Watts, Amperes. Even those don't really exist in nature.
Volta, Watts and Ampere all started from not having a number, to having a number. Those numbers made math and engineering possible. I love numbers, but just because I have a number, does not mean I have a quality associated with it.
That's the next step, and that's where I think we fumble.
Erik - how do you figure 1 Ampere at 1 watt has a S/N of 90dB? There is no S/N correlation between Amperes and Watts.
Sorry for the confusion, I meant Amplifier. :)
For instance, one amp at 1 watt has a S/N ratio of 90 dB.
Though I think when these are taken, it really should be at 2.83V, not 1 Watt.
Best,
E