I have a timeseries data set that converges to the exact (attached). I would like to have some sort of tolerance in my programs but would like to do it numerically. It would be something like min(max(distance_from_exact_of_timeseries)). It is difficult to explain but I hope the picture will help. If I fit a linear regression line to the data I get something along the lines of what I am looking for but I can only do this with the tools after the program has run which defies the point.