To use function from library script, you should use "use" operator in your transformation script, like following:

use LibraryScript;

return library_function($1);

assuming you have script in library named LibraryScript like this:

sub library_function(x)
{
   return x * 2;
}

Best regards,
Victor

1. enter the script directly to the transformation as you would while editing script in script library
2. create function in the script library and just use it in the transformation window
   e.g. in script library:

sub function(x)
{code}

in tranformation tab: function(inputdata);

Will try it to be sure..

EDIT:
forgot we discussed transformations in thread History management : store averaged values ?

also did a little dummy transformation "return (2 * GetDCIValue($node, FindDCIByDescription($node, "CPU 47")));" which returns twice the value of the DCI "CPU 47" and it works fine as I suggested above

With regards,
Milan Sperl