Here is quick run down of the buttons
Left & Right arrows:
Boost Channel 1, 2, 3, External, Warning, and Off.
When boost channel 1,2,3 is selected - Hold down knob for 5 seconds or more to configure how much boost 'rate'. Press the knob once again to select the channel, then twist it to adjust the rate.
If you hold the knob down down again for 5 secs or more, it allows you to adjust boost 'gain' across all channels.
I have gain set to '15' and rate to '65' to achieve 16PSI / 1.1bar on a SR20.
Warning - will start beeping/flashing if boost exceeds the level you specifiy.
Pressing left & right together will reset peak boost reading.