about the 3ddot

Hi AFNI experts,
I noticed that 3ddot output different values when the -demean option is on or off.
I guess that the output without -demean is not the person correlation.

the help documentation say the following:
-demean Means to remove the mean from each volume
prior to computing the correlation.

What is the meaning of the output value if I did not use the -demean option?

Thanks very much!

For Pearson correlation, you do need to add the -demean option to get the proper result. Without the option, it presumes that the means for the two variables are 0.