This can be done either by using interpolation or approximation (regression).
Which one would you prefer?
The problem is that for any interpolation X has to be sorted in ascending order with no duplicate values.
You have a lot of duplicates in your vector X.
E.g. your first values in X are all 6 380 0000 which will make the interpolation to throw an error. The corresponding values in Y are different, so what result would you expect for y(63800000)? You have the choice from -0.0325 downto -0.0312.