Matching MixBus level with track channel during calibration.

[ODC]

Hi everyone et bonsoir de Paris !

I've been experiencing some strange readings when recalibrating my rig last night.
I use an old Adat bridge (16bit) as my master output then go to a small mixer for listening.
I have a pair of Dorrough meters (40-C2) and a DK MSD600 for monitoring levels.
What I did first was pluging one of the Adat bridge's outputs directly into one Dorrough meter.
The Adat bridge is calibrated to +4dBu using internal PT option.
I've inserted Generator X plug for generating the Test tone on the master bus.
I fed the meter with a -18dBFS, 1000Hz sine wave and adjust the trim pot to 0dB AVG.
Then, by curiosity, I did the same technique, inserting the test tone in a track channel.
Problem is the levels didn't match !
I've called Digi france today and the guy told me they are aware of this problem !!!
Could someone explain this to me ? Dave, Nika ?
Et merci d'avance !