Harry
You may find the various videos on line helpful. This one explains the settings available via the software or on the programming box. The first half of the video you can skip past as its covers downloading the software.
The gain is a percentage that you can set separately for each axis. It can be adjusted for response rate and servo speed. The gyro as I understand it works by adjusting the surface to counteract the forces on the airframe that are causing uncommanded movement. If the amount of counter movement it produces is too high the wings, in the case of the ailerons will waggle and look like they are fluttering. Turning the variable gain down will stop this happening. However, you may like to takeoff and land with higher gyro gain setting and you can adjust the gain on the Tx accordingly. Strictly speaking the best way for a gyro to act is to vary the amount of gain by the airspeed. I am not aware of any gyro that works this way. I have found that approx 25% gain is a comfortable figure.
Now with a 3 axis gyro you need to adjust the gain separately for each axis to be sure you have it as you prefer. In this case you can set the 3 position mode switch up to help. It is freely assignable. The user defined mode allows you to select each axis separately one for each switch position,. This can allow you to determine the amount of gain you need for each axis by switching to each in turn and varying the gain and watching the action of the plane. Then when you land you can set the gain to different values for each axis, so each axis will be at optimum setting at the same overall gain setting when all axis are operative together.
I have used ACT gyros for many years on ailerons and this Hobby Eagle one works the same way and results are pretty much the same. In fact we flew the Huckebein with an ACT gyro first and I fitted the Hobby Eagle gyro in its place and flew it. I was concerned about the way the plane would respond and takeoff was with no gyro but soon after takeoff it proved necessary to have the aileron gyro on to stabilise it as the plane was really unstable. Turning the ailerons gyro on first was immediately better with the wings stable, but the plane must have been slightly tail heavy as it was sitting back and squirming about. Turning the full 3 axis made it instantly stable.
Hope this helps.
John