I want to highlight what Sandeep is asking. He is asking to plot the time series of correlation which is defined for the window of 21 years. it is similar like running trend. So it will show the variation of correlation in the window of 21 year for the time period used in the analysis.
I also searched a lot for running trend in ferret but I found its very cumbersome in ferret.
What did you find which is cumbersome? Do you mean that it's significantly more complicated than when you calculate the non-"running" correlation coefficient?
I've never calculated running correlation coefficients, but I have calculated running standard deviation, which is straightforward, because the codes for the "running" and non-"running" versions are almost the same. The running version uses a moving window through @SBX, which is the only difference.