I just recently put up a new Tipper. I have a few of them and overhaul for ready replacement. Never noticed when first put up the screws were spun way up.
I have been monitoring over that last several weeks with different types of rain events.
The screws are pretty close now. I monitor over 5 to 10 rain events to see if it stays plus or minus. I find there are variances depending on type of event.
Probably no single event should be taken as the only calibration point, rather, an average performance over several storms.
While true some single days may show skewed data, the history will be true over time.