Hi all, The square root external function is linked to the Ferret External Functions web page. Look for it at the very bottom of http://www.ferret.noaa.gov/Ferret/External_Functions/ferret_EF.html but it really is just a demonstration function. There is no reason to use anything but the exponent 0.5. This can apply to any variable, from a scalar value to a multi-dimensional variable. In my mail tool, it was hard to see the syntax of the previous answers. You use the carat symbol, yes? let S = var^0.5 Please see the index entry "Operators" in the index the Ferret Users Guide for a list of all the operators available in Ferret: http://www.ferret.noaa.gov/Ferret/Documentation/Users_Guide/current/fer_html.htm Jaison Kurian wrote: Hi, You can find the sqare root of a variable xx in ferret as xx^0.5. yes? let xx = 100 yes? let yy = xx^0.5 yes? list yy VARIABLE : XX^0.5 10.00 An external function (fortran subroutine, sqrt.F) is given at http://ferret.wrc.noaa.gov/Ferret/External_Functions/contributions/sqrt.F. But that external function is not there with FERRET v5.53/v.5.5. May be somebody else can help you to use that subroutine as an external function. With Regards Jason |