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I've often wondered how relative the metering is between the different sound cards, pc sytems and such. So many variables, so I've never relied on the accuracy of the meters exclusively.

The math going on inside the DAW has nothing to do with the sound card, system, monitors etc ..
Inside the DAW itself it is all digital, so nothing really magical about it, simply math. It happens before the signal ever gets sent to the sound card.

We live in a wondrous age for recording.
By being able to measure the RMS, peak, average, and Peak/Average ratio we can get a pretty honest measurement of how 'loud' our mix is regardless of the system. Sure, System A may be louder/better than System B, but the goal is to make them both respond as expected.

The same two songs on system A can be reliably relevant on system B if the measurements/adjustments happen before the sound ever gets produced on either system.
Just my 2 bits.

I do not work here, but the benefits are still awesome
Make your sound your own!