Tested all surfaces. Vertical without discrepancies. Horizontal from a distance of 10 meters: The bottom plane is almost ideal; The upper one is within the limits of the passport error (if desired, it can be adjusted). The tripod is not needed "liquid", since the weight of the device is tangible. To sum up: a pretty decent thing for a reasonable price. Thanks to the seller! P. s. Added a photo with a calibrated upper horizon. The process itself is quite affordable. Adjusting screws for a small hexagon.