The level settings can be found in the preferences menu. Here you can adjust the response time and the level range. The preferences menu offers three response modes: impulse (35 ms), fast (125 ms) and slow (1 s).
For an uncalibrated device a level of 0 dB is the full scale maximum. However if you calibrated your device to a defined level of your hardware environment you might observe values above that range if clipping occurs (in that case you should decrease the gain/level of your hardware and calibrate again).
The peaks are indicated by horizontal lines, which inertially adapt to the current level over time (making them easily readable).