Use the BGC 2.2 software and you will also get a lot more options you can play with.
The software makes things a bit more accurate as you can line up the sensors to the level position before hitting the calibrate button(this is supposed to help stop it drifting over time)
It says that when calibrating, the further the sensors are away from their level lined up state, the more it starts to drift over time.
Here is the link...You want the 2.2b version
http://www.basecamelectronics.com/downloads/8bit/Obviously you will need to connect to the computer using the gimbal usb.
Then select the 'comm port' and press 'connect or open'
Then you need to 'read' your settings so it copies them to the software before making adjustments and when finished 'write' back to the gimbal(much the same as with the 380 software)
There is a manual as well with that can be looked at and is very long winded....but basically the blue arrows on all the dials wants to be lined up with the blue marker at the bottom, and it reading 0.0 when you hit the cal button.
After the cal is done you can click that button on the board once at set the angle you want it at.