You need an SPL meter. If you want to be calibrated to what's called, "Reference Level" you set each speaker to measure 75 dB on the meter. If your system can not reach that level then just set them so they are all the same level on the meter. If you don't have an SPL meter then you just adjust them so they sound about the same level. Depending on the sensitivity of each speaker, the dB setting on the menu could be anything. Like speakers should be the same, for example the left and right main should be the same setting but the center might be completely different. Similarly the left and right surround should be the same but these may be completely different from the mains. The key is to make them all sound the same level.