From the Yamaha guys (Trainers on The Road) who do the the PM5D/M7 Classes :
" So where is the unity point on my digital meters? "
" The unity point on your digital console will vary by manufacturer. However, on almost all of the newer Yamaha digital consoles, the unity point is found at -20dBFS. The only exceptions are the DM2000, and 02R. On these units, the unity point is found at -14dBFS.
The unity point we are talking here is the internal signal level of consoles when the consoles output +4dBu (0VU). This is the reference level of most equipment we use. Which means, when you see -20dBFS on your output meter of your M7CL, the console outputs signal of +4dBu."