The VU meter’s needle takes about 300 milliseconds to reach its reading, and that sluggishness is the design. Averaging over a third of a second, it ignores momentary spikes and reports something close to how loud the material feels, which made it the broadcast and studio standard for decades.
Its ballistics are why it reads musically: the needle leans into a chorus and relaxes in a verse, more like a listener than an instrument.
The VU’s descendants split its job: RMS and LUFS meters took the loudness question, peak hold took the safety question. The needle survives as interface iconography and in control rooms where its particular honesty is still trusted.