If seen some programs define the level 100 to be 0dB. But in my opiniun this is wrong becuase the dB is something that changes when you turn the volume of your sound card/stereo up.
Some also define the maximum as 0dB.
And BTW these values can also be seen as an offset of the real dB values outputted by your soundcard/stereo.
Hope this helps a bit.
Greetings me.