Hi Ferret Users, Has anyone created external functions for doing more sophisticated filtering (bandpass filters) such as a Blackmon filter, one such as described in Doblas-Reyes AND Deque in Monthly Weather Review Dec 1998, a Lanczos type filter, or some other? Thanks. Cheers, Brent -- Brent A. McDaniel Dept of Earth and Atmospheric Sciences Georgia Institute of Technology Atlanta, Ga. USA