### 16.1. If different software packages produce different InChIs, which is the trusted one?

As many software vendors and open-source teams have built the InChI functionality into their own programs (typically through InChI API library calls), cases appear of producing different InChI strings for the same compound when using different software. 

This may be related to application of different algorithms for input data pre-treatment, especially the interpretation of source drawing/file format or pre-normalization of structures before calling InChI procedures. (A quite illustrative example related to the perception of poorly drawn stereo may be found at http://sourceforge.net/mailarchive/message.php?msg_id=28013563).

**The ultimate reference is, in any case, the InChI string produced by the executable inchi-1 (either under MS Windows or Linux) of the current InChI Software released by IUPAC/InChI Trust.**

If your chemistry software of choice does provide some unexpected/undesirable InChI strings, please check if this behavior can be reproduced by the inchi-1 executable.