They are not likely out of calibration, they are just showing different things. The mechanical VU meters have slow ballistics so that they read a quasi-average (
RMS)
level that more closely represents how loudness is perceived. The
LED meters are fast, peak reading meters. Peak audio levels are anywhere from 12 to 20 dB higher than VU
level with typical audio that has not been compressed or limited. Consequently, with real audio applied, the
LED meters will always read higher than VU meters. If you were to check them using
sine wave tone, they would compare quite closely.
VU meters are the standard for broadcast and, in some cases, recording to get fairly consistent loudness. The LEDs are a good tool for preventing
clipping and the resulting
distortion. Often, the two are used together as your ML3000 does.
It is also worth mentioning that there can be
LED meters with VU like ballistics, although they would not do that alongside mechanical meters. There are also
LED meters that display both VU and peak levels simultaneously. such as the famous Dorrough meters. Those are rare due to their complexity.
