What do the two scales on the master meter represent?

The numbers on the left show the fader setting. 0dB is unity gain, which means that the input level is the same as the output level.  In the image below, 6 is -6dB of gain on the fader. The numbers on the right are the scale for the meters. In this image, the audio is a normalized sine wave. The fader is set to -6 dB, and the metering shows the audio playback is at -6dB as well.