If the MASTER OUT [ATT.] is set to 0 dB, the MASTER1 output (XLR) will be +4 dBu when the master level indicator 0 is lit, and the MASTER2 output (RCA) will be 0 dBu.

If the [REFERENCE LEVEL] of the DIGITAL MASTER OUT is set to -21 dBFS, the DIGITAL MASTER output level will be -21 dBFS when the master level indicator 0 is lit.

Note that even if you adjust the [ATT.] of the MASTER OUT and DIGITAL MASTER OUT, the master level indicator doesn't change.