The usual regressio or correlation analysis uses a straight line
relationship between the two variables
Y = a+bX.
The Climate Explorer fit routine can also fit other functions, such
as the parabola
Y = a+bX(1+cX).
In this case the correlation indicates the correlation between the
fitted right-hand side and Y and is therefore always positive.
For correlations between two time series, a cubic fit (Y = a+BX+cX²+dX³) and a
straight line plus time derivative (Y =
a+bX+cY') are also available.
The option "phase diagram" does not perform a fit and connects all
(Xi,Yi) pairs by a line.