STDDEV is an IDL standard library routine that is defined in the file "stddev.pro" located under the "lib" subdirectory of an IDL installation. However, an error like above can happen if a user modifies/customizes their IDL program file search path ("IDL_PATH" preference or the underlying "!PATH" IDL system variable) setting but does not include the standard IDL library file location. To avoid this type of problem, when modifying your IDL program file search path, be sure to also include the "" token to specify the standard IDL library files. For example, using PREF_SET at the IDL> command prompt: IDL> PREF_SET, 'IDL_PATH', ''+PATH_SEP(/SEARCH_PATH)+'/path/to/my/idl/lib' Here are links to pages on the Exelis VIS web site that provide additional information about the topics in this forum post: Documentation Center: STDDEV http://www.exelisvis.com/docs/STDDEV.... Documentation Center: IDL_PATH http://www.exelisvis.com/docs/prefs_d... "Quick tips for customizing your IDL program search path" http://www.exelisvis.com/Support/Help...

I triggered this post with a request to Tech Support. Relatively new to IDL, I was unaware of the consequences of using a SAV file from another source. I had been given a sav file to use as I learned IDL, and IT contained a !path variable. After I read this thread, I tracked down the path (sigh, after repairing the entire installation ;-(, and discovered that I had the correct path at IDL startup, and the wrong path after loading the sav file. I now localPath = !path restore, ... !path = localPath ... and this fixes the problem. Thanks to IDL TS for this tip. ~R~