A way to set your UO accurately:
1)
https://osu.ppy.sh/s/4659 The offset wizard. But change it so it has 120 beats and OD0 (this allows to have more accurate results).
2) Change your UO to a high number (for example +50), that way in the results screen you get something (-0ms ~ +45ms) (with all the hit errors in one side, so you know the average of the hit errors instead of the average of the late hits and average of early hits).
3) Play the map with your eyes closed (so your vision doesn't mess you up when seeing how off the approach circles are), trying to make the hit-sounds sync with the sounds of the beatmap.
4) In the average hit errors, you should get something like (-0ms ~ +45ms). Subtract the average error (45) to your current UO (50 in example) and you get the estimation of the correct UO.
Then, multiply your Unstable Rate by 0.0238969 to get the estimated error of the measurement of the correct UO.
(If you used a version of the map with only 29 beats, you multiply the UR by 0.0513125 instead).
Example: With starting UO of 70ms, getting (-0ms ~ +60ms) average hit errors and 90 Unstable Rate.
Then the estimated correct UO is +10ms, with an error of 2.15ms. UO: +10ms±2.15ms.
So, the lower is your unstable rate, the more accurately you can estimate the correct UO.
