What is the name of the tool?

Back in the '80's I had a VU/RMS LED display that 'tracked' either with reasonable accuracy.  Was 'bout 2"h.x9"w.x6"d. ....

VU was easy, a line input wherever you wanted to tap in.

RMS?  Forget how that was accomplished, but 30+ years wipes some details away....  But it did illustrate that 1 watt (average) into a living room could be loud enough....

The 'peak' readings, however, could be pretty substantial.  150 peaks could drive one out of the room...

Merry Post-New Year....

"....you're probably wondering why I'm here...and so am I...."

https://www.thezappamovie.com/ 

"...not that it makes a hellava lot of difference to you...."

I was going to write something rude. Instead why do you need a wattage meter?

db, as in decibel, meter