[SWRocket]

Originally Posted by ctrlz

Not sure how knowing a number reading on the audio will help tune an aftermarket system. If this is important send a test tone and adjust volume until peak-to-peak voltage is within range.

It's important because when you take measurements with an RTA and mic, you want to make sure the HU level is the same. So if I manage to get all my tuning done in one session, it's not an issue. But that's unlikely.
More likely, I will have to do it over several sessions spanning a couple of days and leaving the car on that whole time is not practical.
I may just use that startup volume feature (which I forgot about so thanks for reminding me) as I only need about 80-85db for measurements.

Another reason it matters is for setting gains. When you set gains you need to know at what volume the HU clips. Now, the HU may be able to go to max volume without clipping and this will not matter, but if it does clip, knowing the max volume before clipping is crucial.