So far I learned that arming for 20sec enters one of those.
Then you should fly in windless conditions.
Wiki says: "Once you are flying perfectly level, simply land the copter and wait out the remaining time. The accelerometer offsets will be overwritten. The LEDs will cycle for the entire 45 seconds."
The questions are:
1- should you just hover above as tight space as possibly, ?
2.- or should your priority be to keep it absolutely still in air ?
3.- any other suggestions ?
4.-is it better than levelling using a levelling tool across the quad's arms and shimming up the quad ?