Mine drifts for about 40cm from the takeoff point and then it does this rotation to the right, it is very very slow.

Thanks for bringing to our attention Quorum. Per it, how about trying the method below?
1) Calibrate IMU
2)  Calibrate the center of gravity while hovering in the air.
3)  Fly in an open area on a sunny day.
If persists, could you kindly a video show this issue, plus screenshots of firmware version and APP version for further analysis?

RYZE Posted at 2-16 20:59
Thanks for bringing to our attention Quorum. Per it, how about trying the method below?
1) Calibrate IMU
2)  Calibrate the center of gravity while hovering in the air.

yes doing these fixed the issue.

Guorium Posted at 2-16 22:34
yes doing these fixed the issue.

Great to here, enjoy the Tello, it is an awesome little drone