n-Track 6.0 and later supports the K-System for monitoring signal levels (with presets for K-12, K-14 and K-20 modes).
By default the master playback meters show a pair of meters for each channel. The inner meter shows the Peak level, while the outer meter shows RMS level.
You can change the vu meter setting to show only peak or RMS meters in the popup menu that appears right clicking on the vu meter window.
You can find more info on the K-System clicking here.
If you want all the technical details read Bob Katz article