BaseElements will also sort through all of your calculations and record where you are using Plugins or Variables. There is a count of both of these items on the File layout and you can click directly into any one to see exactly where it's used.
Also any Plugins or Variables used by a calculation or any other item will also be listed on the "Items Used" tab.
Plugins are not distinguished by the DDR as separate function calls, so there is extra processing in the import process to break out any internal functions and leave behind only external plugin related functions.
And Variables are not broken out of the calculation at all, so after the calculation import is complete we actually process the text inside the calculations to strip out the variables used. The code to do this is not part of the DDR or of FileMaker's calculation engine, so it may not pick up variables using complex characters or names. Technically it's possible to have all sorts of strange characters in variable names, but we suggest you keep them limited to basic ascii to make things easier.